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1579 lines
35 KiB
Markdown
1579 lines
35 KiB
Markdown
![]() |
# V Documentation
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## Introduction
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V is a statically typed compiled programming language designed for building maintainable software.
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It's similar to Go and is also influenced by Oberon, Rust, Swift.
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V is a very simple language. Going through this documentation will take you about half an hour,
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and by the end of it you will learn pretty much the entire language.
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Despite being simple, it gives a lot of power to the developer. Anything you can do in other languages,
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you can do in V.
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## Hello World
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```v
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fn main() {
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println('hello world')
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}
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```
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Functions are declared with `fn`. Return type goes after the function
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name. In this case `main` doesn't return anything, so the type is
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omitted.
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Just like in C and all related languages, `main` is an entry point.
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`println` is one of the few built-in functions. It prints the value
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to standard output.
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`fn main()` declaration can be skipped in one file programs.
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This is useful when writing small programs, "scripts", or just learning
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the language. For brevity, `fn main()` will be skipped in this
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tutorial.
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This means that a "hello world" program can be as simple as
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```v
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println('hello world')
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```
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## Comments
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```v
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// This is a single line comment.
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/* This is a multiline comment.
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/* It can be nested. */
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*/
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```
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## Functions
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```v
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fn main() {
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println(add(77, 33))
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println(sub(100, 50))
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}
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fn add(x int, y int) int {
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return x + y
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}
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fn sub(x, y int) int {
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return x - y
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}
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```
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Again, the type comes after the argument's name.
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Just like in Go and C, functions cannot be overloaded.
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This simplifies the code and improves maintainability and readability.
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Functions can be used before their declaration:
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`add` and `sub` are declared after `main`, but can still be called from `main`.
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This is true for all declarations in V and eliminates the need of header files
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or thinking about the order of files and declarations.
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```v
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fn foo() (int, int) {
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return 2, 3
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}
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a, b := foo()
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println(a) // 2
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println(b) // 3
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```
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Functions can return multiple values.
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Functions, like consts, and types, are private (not exported) by default.
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To allow other modules to use them, prepend `pub`. The same applies
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to consts and types.
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```v
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pub fn public_function() {
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}
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fn private_function() {
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}
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```
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## Variables
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```v
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name := 'Bob'
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age := 20
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large_number := i64(9999999999)
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println(name)
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println(age)
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println(large_number)
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```
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Variables are declared and initialized with `:=`. This is the only
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way to declare variables in V. This means that variables always have an initial
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value.
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The variable's type is inferred from the value on the right hand side.
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To force a different type, use type conversion:
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the expression `T(v)` converts the value `v` to the
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type `T`.
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Unlike most other languages, V only allows defining variables in functions.
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Global (module level) variables are not allowed. There's no global state in V.
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```v
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mut age := 20
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println(age)
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age = 21
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println(age)
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```
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To change the value of the variable use `=`. In V, variables are
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immutable by default. To be able to change the value of the variable, you have to declare it with `mut`.
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Try compiling the program above after removing `mut` from the first line.
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Please note the difference between `:=` and `=`
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`:=` is used for declaring and initializing, `=` is used for assigning.
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```v
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fn main() {
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age = 21
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}
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```
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This code will not compile, because variable `age` is not declared.
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All variables need to be declared in V.
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```v
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fn main() {
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age := 21
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}
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```
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In development mode this code will result in an "unused variable" warning.
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In production mode (`v -prod foo.v`) it will not compile at all, like in Go.
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```v
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fn main() {
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a := 10
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if true {
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a := 20
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}
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}
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```
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Unlike most languages, variable shadowing is not allowed. Declaring a variable with a name that is already used in a parent scope will result in a compilation error.
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## Basic types
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```v
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bool
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string
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i8 i16 int i64 i128 (soon)
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byte u16 u32 u64 u128 (soon)
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rune // represents a Unicode code point
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f32 f64
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byteptr
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voidptr
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```
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Please note that unlike C and Go, `int` is always a 32 bit integer.
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## Strings
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```v
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name := 'Bob'
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println('Hello, $name!') // `$` is used for string interpolation
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println(name.len)
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bobby := name + 'by' // + is used to concatenate strings
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println(bobby) // "Bobby"
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println(bobby[1..3]) // "ob"
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mut s := 'hello '
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s += 'world' // `+=` is used to append to a string
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println(s) // "hello world"
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```
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In V, a string is a read-only array of bytes. String data is encoded using UTF-8.
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Strings are immutable.
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Both single and double quotes can be used to denote strings. For consistency,
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`vfmt` converts double quotes to single quotes unless the string contains a single quote character.
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Interpolation syntax is pretty simple. It also works with fields:
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`'age = $user.age'`. If you need more complex expressions, use `${}`: `'can register = ${user.age > 13}'`.
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All operators in V must have values of the same type on both sides. This code will not compile if `age` is an `int`:
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```v
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println('age = ' + age)
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```
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We have to either convert `age` to a `string`:
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```v
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println('age = ' + age.str())
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```
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or use string interpolation (preferred):
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```v
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println('age = $age')
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```
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To denote character literals, use `
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```v
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a := `a`
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assert 'aloha!'[0] == `a`
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```
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For raw strings, prepend `r`. Raw strings are not escaped:
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```v
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s := r'hello\nworld'
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println(s) // "hello\nworld"
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```
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## Arrays
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```v
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mut nums := [1, 2, 3]
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println(nums) // "[1, 2, 3]"
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println(nums[1]) // "2"
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nums << 4
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println(nums) // "[1, 2, 3, 4]"
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nums << [5, 6, 7]
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println(nums) // "[1, 2, 3, 4, 5, 6, 7]"
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mut names := ['John']
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names << 'Peter'
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names << 'Sam'
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// names << 10 <-- This will not compile. `names` is an array of strings.
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println(names.len) // "3"
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println('Alex' in names) // "false"
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names = [] // The array is now empty
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// We can also preallocate a certain amount of elements.
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ids := [0].repeat(50) // This creates an array with 50 zeros
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```
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Array type is determined by the first element: `[1, 2, 3]` is an array of ints (`[]int`).
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`['a', 'b']` is an array of strings (`[]string`).
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All elements must have the same type. `[1, 'a']` will not compile.
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`<<` is an operator that appends a value to the end of the array.
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It can also append an entire array.
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`.len` field returns the length of the array. Note, that it's a read-only field,
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and it can't be modified by the user. All exported fields are read-only by default in V.
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`val in array` returns true if the array contains `val`.
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All arrays can be easily printed with `println(arr)` and converted to a string
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with `s := arr.str()`.
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Arrays can be efficiently filtered and mapped with `.filter()` and
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`.map()` methods:
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```v
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nums := [1, 2, 3, 4, 5, 6]
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even := nums.filter(it % 2 == 0)
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println(even) // [2, 4, 6]
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words := ['hello', 'world']
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upper := words.map(it.to_upper())
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println(upper) // ['HELLO', 'WORLD']
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```
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`it` is a special variable that refers to an element in filter/map methods.
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## Maps
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```v
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mut m := map[string]int // Only maps with string keys are allowed for now
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m['one'] = 1
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m['two'] = 2
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println(m['one']) // "1"
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println(m['bad_key']) // "0"
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println('bad_key' in m) // Use `in` to detect whether such key exists
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m.delete('two')
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numbers := {
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'one': 1,
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'two': 2,
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}
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```
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## If
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```v
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a := 10
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b := 20
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if a < b {
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println('$a < $b')
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} else if a > b {
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println('$a > $b')
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} else {
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println('$a == $b')
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}
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```
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`if` statements are pretty straightforward and similar to most other languages.
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Unlike other C-like languages, there are no parentheses surrounding the condition, and the braces are always required.
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`if` can be used as an expression:
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```v
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num := 777
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s := if num % 2 == 0 {
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'even'
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}
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else {
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'odd'
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}
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println(s) // "odd"
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```
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## In operator
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`in` allows to check whether an array or a map contains an element.
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```v
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nums := [1, 2, 3]
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println(1 in nums) // true
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m := {'one': 1, 'two': 2}
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println('one' in m) // true
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```
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It's also useful for writing more clear and compact boolean expressions:
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```v
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if parser.token == .plus || parser.token == .minus ||
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parser.token == .div || parser.token == .mult {
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...
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}
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if parser.token in [.plus, .minus, .div, .mult] {
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...
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}
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```
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V optimizes such expressions, so both `if` statements above produce the same machine code, no arrays are created.
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## For loop
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V has only one looping construct: `for`.
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```v
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numbers := [1, 2, 3, 4, 5]
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for num in numbers {
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println(num)
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}
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names := ['Sam', 'Peter']
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for i, name in names {
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println('$i) $name') // Output: 0) Sam
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} // 1) Peter
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```
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The `for value in` loop is used for going through elements of an array.
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If an index is required, an alternative form `for index, value in` can be used.
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Note, that the value is read-only. If you need to modify the array while looping, you have to use indexing:
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```v
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mut numbers := [1, 2, 3, 4, 5]
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for i, num in numbers {
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println(num)
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numbers[i] = 0
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}
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```
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```v
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mut sum := 0
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mut i := 0
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for i <= 100 {
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sum += i
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i++
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}
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println(sum) // "5050"
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```
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This form of the loop is similar to `while` loops in other languages.
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The loop will stop iterating once the boolean condition evaluates to false.
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Again, there are no parentheses surrounding the condition, and the braces are always required.
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```v
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mut num := 0
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for {
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num++
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if num >= 10 {
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break
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}
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}
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println(num) // "10"
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```
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The condition can be omitted, this results in an infinite loop.
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```v
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for i := 0; i < 10; i++ {
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// Don't print 6
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if i == 6 {
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continue
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}
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println(i)
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}
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```
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Finally, there's the traditional C style `for` loop. It's safer than the `while` form
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because with the latter it's easy to forget to update the counter and get
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stuck in an infinite loop.
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Here `i` doesn't need to be declared with `mut` since it's always going to be mutable by definition.
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## Match
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```v
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os := 'windows'
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print('V is running on ')
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match os {
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'darwin' { println('macOS.') }
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'linux' { println('Linux.') }
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else { println(os) }
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}
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s := match number {
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1 { 'one' }
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2 { 'two' }
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|
else {
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println('this works too')
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'many'
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}
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}
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```
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A match statement is a shorter way to write a sequence of `if - else` statements.
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When a matching branch is found, the following statement block will be run, and the final expression will be returned.
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The else branch will be evaluated when no other branches match.
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|
|
||
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```v
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enum Color {
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red
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blue
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green
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}
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||
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||
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fn is_red_or_blue(c Color) bool {
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return match c {
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.red { true }
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.blue { true }
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else { false }
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}
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}
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```
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||
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A match statement can also be used to branch on the variants of an `enum`
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by using the shorthand `.variant_here` syntax.
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||
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|
||
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## Structs
|
||
|
|
||
|
```v
|
||
|
struct Point {
|
||
|
x int
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||
|
y int
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||
|
}
|
||
|
|
||
|
p := Point{
|
||
|
x: 10
|
||
|
y: 20
|
||
|
}
|
||
|
println(p.x) // Struct fields are accessed using a dot
|
||
|
```
|
||
|
|
||
|
Structs are allocated on the stack. To allocate a struct on the heap
|
||
|
and get a reference to it, use the `&` prefix:
|
||
|
|
||
|
```v
|
||
|
// Alternative initialization syntax for structs with 3 fields or fewer
|
||
|
p := &Point{10, 10}
|
||
|
// References have the same syntax for accessing fields
|
||
|
println(p.x)
|
||
|
```
|
||
|
|
||
|
The type of `p` is `&Point`. It's a reference to `Point`.
|
||
|
References are similar to Go pointers and C++ references.
|
||
|
|
||
|
V doesn't have subclassing, but it supports embedded structs:
|
||
|
|
||
|
```v
|
||
|
// TODO: this will be implemented later
|
||
|
struct Button {
|
||
|
Widget
|
||
|
title string
|
||
|
}
|
||
|
|
||
|
button := new_button('Click me')
|
||
|
button.set_pos(x, y)
|
||
|
|
||
|
// Without embedding we'd have to do
|
||
|
button.widget.set_pos(x,y)
|
||
|
```
|
||
|
|
||
|
## Access modifiers
|
||
|
|
||
|
Struct fields are private and immutable by default (making structs immutable as well).
|
||
|
Their access modifiers can be changed with
|
||
|
`pub` and `mut`. In total, there are 5 possible options:
|
||
|
|
||
|
```v
|
||
|
struct Foo {
|
||
|
a int // private immutable (default)
|
||
|
mut:
|
||
|
b int // private mutable
|
||
|
c int // (you can list multiple fields with the same access modifier)
|
||
|
pub:
|
||
|
d int // public immmutable (readonly)
|
||
|
pub mut:
|
||
|
e int // public, but mutable only in parent module
|
||
|
__global:
|
||
|
f int // public and mutable both inside and outside parent module
|
||
|
} // (not recommended to use, that's why the 'global' keyword
|
||
|
// starts with __)
|
||
|
```
|
||
|
|
||
|
For example, here's the `string` type defined in the `builtin` module:
|
||
|
|
||
|
```v
|
||
|
struct string {
|
||
|
str byteptr
|
||
|
pub:
|
||
|
len int
|
||
|
}
|
||
|
```
|
||
|
|
||
|
It's easy to see from this definition that `string` is an immutable type.
|
||
|
The byte pointer with the string data is not accessible outside `builtin` at all.
|
||
|
`len` field is public, but not mutable:
|
||
|
|
||
|
```v
|
||
|
fn main() {
|
||
|
str := 'hello'
|
||
|
len := str.len // OK
|
||
|
str.len++ // Compilation error
|
||
|
}
|
||
|
```
|
||
|
|
||
|
## Methods
|
||
|
|
||
|
```v
|
||
|
struct User {
|
||
|
age int
|
||
|
}
|
||
|
|
||
|
fn (u User) can_register() bool {
|
||
|
return u.age > 16
|
||
|
}
|
||
|
|
||
|
user := User{age: 10}
|
||
|
println(user.can_register()) // "false"
|
||
|
|
||
|
user2 := User{age: 20}
|
||
|
println(user2.can_register()) // "true"
|
||
|
```
|
||
|
|
||
|
V doesn't have classes. But you can define methods on types.
|
||
|
|
||
|
A method is a function with a special receiver argument.
|
||
|
|
||
|
The receiver appears in its own argument list between the `fn` keyword and the method name.
|
||
|
|
||
|
In this example, the `can_register` method has a receiver of type `User` named `u`.
|
||
|
The convention is not to use receiver names like `self` or `this`,
|
||
|
but a short, preferably one letter long, name.
|
||
|
|
||
|
## Pure functions by default
|
||
|
|
||
|
V functions are pure by default, meaning that their return values are only determined by their arguments,
|
||
|
and their evaluation has no side effects.
|
||
|
|
||
|
This is achieved by lack of global variables and all function arguments being immutable by default,
|
||
|
even when references are passed.
|
||
|
|
||
|
V is not a pure functional language however.
|
||
|
It is possible to modify function arguments by using the same keyword `mut`:
|
||
|
|
||
|
```v
|
||
|
struct User {
|
||
|
mut:
|
||
|
is_registered bool
|
||
|
}
|
||
|
|
||
|
fn (u mut User) register() {
|
||
|
u.is_registered = true
|
||
|
}
|
||
|
|
||
|
mut user := User{}
|
||
|
println(user.is_registered) // "false"
|
||
|
user.register()
|
||
|
println(user.is_registered) // "true"
|
||
|
```
|
||
|
|
||
|
In this example, the receiver (which is simply the first argument) is marked as mutable,
|
||
|
so `register()` can change the user object. The same works with non-receiver arguments:
|
||
|
|
||
|
```v
|
||
|
fn multiply_by_2(arr mut []int) {
|
||
|
for i := 0; i < arr.len; i++ {
|
||
|
arr[i] *= 2
|
||
|
}
|
||
|
}
|
||
|
|
||
|
mut nums := [1, 2, 3]
|
||
|
multiply_by_2(mut nums)
|
||
|
println(nums) // "[2, 4, 6]"
|
||
|
```
|
||
|
|
||
|
Note, that you have to add `mut` before `nums` when calling this function. This makes
|
||
|
it clear that the function being called will modify the value.
|
||
|
|
||
|
It is preferable to return values instead of modifying arguments.
|
||
|
Modifying arguments should only be done in performance-critical parts of your application
|
||
|
to reduce allocations and copying.
|
||
|
|
||
|
For this reason V doesn't allow to modify primitive args like integers, only
|
||
|
complex types like arrays and maps.
|
||
|
|
||
|
Use `user.register()` or `user = register(user)`
|
||
|
instead of `register(mut user)`.
|
||
|
|
||
|
V makes it easy to return a modified version of an object:
|
||
|
|
||
|
```v
|
||
|
fn register(u User) User {
|
||
|
return { u | is_registered: true }
|
||
|
}
|
||
|
|
||
|
user = register(user)
|
||
|
```
|
||
|
|
||
|
## High order functions
|
||
|
|
||
|
```v
|
||
|
fn sqr(n int) int {
|
||
|
return n * n
|
||
|
}
|
||
|
|
||
|
fn run(value int, op fn(int) int) int {
|
||
|
return op(value)
|
||
|
}
|
||
|
|
||
|
fn main() {
|
||
|
println(run(5, sqr)) // "25"
|
||
|
}
|
||
|
```
|
||
|
|
||
|
## References
|
||
|
|
||
|
```v
|
||
|
fn (foo Foo) bar_method() {
|
||
|
...
|
||
|
}
|
||
|
|
||
|
fn bar_function(foo Foo) {
|
||
|
...
|
||
|
}
|
||
|
```
|
||
|
|
||
|
If a function argument is immutable like `foo` in the examples above,
|
||
|
V can pass it by value or by reference. The decision is made
|
||
|
by the compiler, and the developer doesn't need to think about it.
|
||
|
|
||
|
You no longer need to remember whether you should pass the struct by value
|
||
|
or by reference.
|
||
|
|
||
|
There's a way to ensure that the struct is always passed by reference by
|
||
|
adding `&`:
|
||
|
|
||
|
```v
|
||
|
fn (foo &Foo) bar() {
|
||
|
println(foo.abc)
|
||
|
}
|
||
|
```
|
||
|
|
||
|
`foo` is still immutable and can't be changed. For that,
|
||
|
`(foo mut Foo)` has to be used.
|
||
|
|
||
|
In general, V references are similar to Go pointers and C++ references.
|
||
|
For example, a tree structure definition would look like this:
|
||
|
|
||
|
```v
|
||
|
struct Node<T> {
|
||
|
val T
|
||
|
left &Node
|
||
|
right &Node
|
||
|
}
|
||
|
```
|
||
|
|
||
|
## Constants
|
||
|
|
||
|
```v
|
||
|
const (
|
||
|
pi = 3.14
|
||
|
world = '世界'
|
||
|
)
|
||
|
|
||
|
println(pi)
|
||
|
println(world)
|
||
|
```
|
||
|
|
||
|
Constants are declared with `const`. They can only be defined
|
||
|
at the module level (outside of functions).
|
||
|
|
||
|
Constant values can never be changed.
|
||
|
|
||
|
V constants are more flexible than in most languages. You can assign more complex values:
|
||
|
|
||
|
```v
|
||
|
struct Color {
|
||
|
r int
|
||
|
g int
|
||
|
b int
|
||
|
}
|
||
|
|
||
|
fn (c Color) str() string { return '{$c.r, $c.g, $c.b}' }
|
||
|
|
||
|
fn rgb(r, g, b int) Color { return Color{r: r, g: g, b: b} }
|
||
|
|
||
|
const (
|
||
|
numbers = [1, 2, 3]
|
||
|
|
||
|
red = Color{r: 255, g: 0, b: 0}
|
||
|
blue = rgb(0, 0, 255)
|
||
|
)
|
||
|
|
||
|
println(numbers)
|
||
|
println(red)
|
||
|
println(blue)
|
||
|
```
|
||
|
|
||
|
Global variables are not allowed, so this can be really useful.
|
||
|
|
||
|
When naming constants, snake_case must be used.
|
||
|
Many people prefer all caps consts: `TOP_CITIES`. This wouldn't work
|
||
|
well in V, because consts are a lot more powerful than in other languages.
|
||
|
They can represent complex structures, and this is used quite often since there
|
||
|
are no globals:
|
||
|
|
||
|
```v
|
||
|
println('Top cities: $TOP_CITIES.filter(.usa)')
|
||
|
vs
|
||
|
println('Top cities: $top_cities.filter(.usa)')
|
||
|
```
|
||
|
|
||
|
## println
|
||
|
|
||
|
`println` is a simple yet powerful builtin function. It can print anything:
|
||
|
strings, numbers, arrays, maps, structs.
|
||
|
|
||
|
```v
|
||
|
println(1) // "1"
|
||
|
println('hi') // "hi"
|
||
|
println([1,2,3]) // "[1, 2, 3]"
|
||
|
println(User{name:'Bob', age:20}) // "User{name:'Bob', age:20}"
|
||
|
```
|
||
|
|
||
|
If you want to define a custom print value for your type, simply define a
|
||
|
`.str() string` method.
|
||
|
|
||
|
If you don't want to print a newline, use `print()` instead.
|
||
|
|
||
|
## Modules
|
||
|
|
||
|
V is a very modular language. Creating reusable modules is encouraged and is
|
||
|
very simple.
|
||
|
To create a new module, create a directory with your module's name and
|
||
|
.v files with code:
|
||
|
|
||
|
```v
|
||
|
cd ~/code/modules
|
||
|
mkdir mymodule
|
||
|
vim mymodule/mymodule.v
|
||
|
|
||
|
// mymodule.v
|
||
|
module mymodule
|
||
|
|
||
|
// To export a function we have to use `pub`
|
||
|
pub fn say_hi() {
|
||
|
println('hello from mymodule!')
|
||
|
}
|
||
|
```
|
||
|
|
||
|
You can have as many .v files in `mymodule/` as you want.
|
||
|
|
||
|
Build it with `v build module ~/code/modules/mymodule`.
|
||
|
|
||
|
That's it, you can now use it in your code:
|
||
|
|
||
|
```v
|
||
|
module main
|
||
|
|
||
|
import mymodule
|
||
|
|
||
|
fn main() {
|
||
|
mymodule.say_hi()
|
||
|
}
|
||
|
```
|
||
|
|
||
|
Note that you have to specify the module every time you call an external function.
|
||
|
This may seem verbose at first, but it makes code much more readable
|
||
|
and easier to understand, since it's always clear which function from
|
||
|
which module is being called. Especially in large code bases.
|
||
|
|
||
|
Module names should be short, under 10 characters. Circular imports are not allowed.
|
||
|
|
||
|
You can create modules anywhere.
|
||
|
|
||
|
All modules are compiled statically into a single executable.
|
||
|
|
||
|
If you want to write a module that will automatically call some
|
||
|
setup/initialization code when imported (perhaps you want to call
|
||
|
some C library functions), write a module `init` function inside the module:
|
||
|
|
||
|
```v
|
||
|
fn init() int {
|
||
|
// your setup code here ...
|
||
|
return 1
|
||
|
}
|
||
|
```
|
||
|
|
||
|
The init function cannot be public. It will be called automatically.
|
||
|
|
||
|
## Interfaces
|
||
|
|
||
|
```v
|
||
|
struct Dog {}
|
||
|
struct Cat {}
|
||
|
|
||
|
fn (d Dog) speak() string {
|
||
|
return 'woof'
|
||
|
}
|
||
|
|
||
|
fn (c Cat) speak() string {
|
||
|
return 'meow'
|
||
|
}
|
||
|
|
||
|
interface Speaker {
|
||
|
speak() string
|
||
|
}
|
||
|
|
||
|
fn perform(s Speaker) {
|
||
|
println(s.speak())
|
||
|
}
|
||
|
|
||
|
dog := Dog{}
|
||
|
cat := Cat{}
|
||
|
perform(dog) // "woof"
|
||
|
perform(cat) // "meow"
|
||
|
```
|
||
|
|
||
|
A type implements an interface by implementing its methods.
|
||
|
There is no explicit declaration of intent, no "implements" keyword.
|
||
|
|
||
|
## Enums
|
||
|
|
||
|
```v
|
||
|
enum Color {
|
||
|
red green blue
|
||
|
}
|
||
|
|
||
|
mut color := Color.red
|
||
|
// V knows that `color` is a `Color`. No need to use `color = Color.green` here.
|
||
|
color = .green
|
||
|
println(color) // "1" TODO: print "green"?
|
||
|
```
|
||
|
|
||
|
## Option/Result types & error handling
|
||
|
|
||
|
```v
|
||
|
struct User {
|
||
|
id int
|
||
|
name string
|
||
|
}
|
||
|
|
||
|
struct Repo {
|
||
|
users []User
|
||
|
}
|
||
|
|
||
|
fn new_repo() Repo {
|
||
|
return Repo {
|
||
|
users: [User{1, 'Andrew'}, User {2, 'Bob'}, User {10, 'Charles'}]
|
||
|
}
|
||
|
}
|
||
|
|
||
|
fn (r Repo) find_user_by_id(id int) ?User {
|
||
|
for user in r.users {
|
||
|
if user.id == id {
|
||
|
// V automatically wraps this into an option type
|
||
|
return user
|
||
|
}
|
||
|
}
|
||
|
return error('User $id not found')
|
||
|
}
|
||
|
|
||
|
fn main() {
|
||
|
repo := new_repo()
|
||
|
user := repo.find_user_by_id(10) or { // Option types must be handled by `or` blocks
|
||
|
return // `or` block must end with `return`, `break`, or `continue`
|
||
|
}
|
||
|
println(user.id) // "10"
|
||
|
println(user.name) // "Charles"
|
||
|
}
|
||
|
```
|
||
|
|
||
|
V combines `Option` and `Result` into one type, so you don't need to decide which one to use.
|
||
|
|
||
|
The amount of work required to "upgrade" a function to an optional function is minimal:
|
||
|
you have to add a `?` to the return type and return an error when something goes wrong.
|
||
|
|
||
|
If you don't need to return an error, you can simply `return none`.
|
||
|
|
||
|
This is the primary way of handling errors in V. They are still values, like in Go,
|
||
|
but the advantage is that errors can't be unhandled, and handling them is a lot less verbose.
|
||
|
|
||
|
`err` is defined inside an `or` block and is set to the string message passed
|
||
|
to the `error()` function. `err` is empty if `none` was returned.
|
||
|
|
||
|
```v
|
||
|
user := repo.find_user_by_id(7) or {
|
||
|
println(err) // "User 7 not found"
|
||
|
return
|
||
|
}
|
||
|
```
|
||
|
|
||
|
You can also propagate errors:
|
||
|
|
||
|
```v
|
||
|
resp := http.get(url)?
|
||
|
println(resp.body)
|
||
|
```
|
||
|
|
||
|
`http.get` returns `?http.Response`. It was called with `?`, so the error is propagated to the calling function
|
||
|
(which must return an optional) or in case of `main` leads to a panic.
|
||
|
Basically the code above is a shorter version of
|
||
|
|
||
|
```v
|
||
|
resp := http.get(url) or {
|
||
|
panic(err)
|
||
|
}
|
||
|
println(resp.body)
|
||
|
```
|
||
|
|
||
|
V does not have a way to force unwrap an optional (like Rust's `unwrap()`
|
||
|
or Swift's `!`). You have to use `or { panic(err) }` instead.
|
||
|
|
||
|
## Generics
|
||
|
|
||
|
```v
|
||
|
struct Repo<T> {
|
||
|
db DB
|
||
|
}
|
||
|
|
||
|
fn new_repo<T>(db DB) Repo<T> {
|
||
|
return Repo<T>{db: db}
|
||
|
}
|
||
|
|
||
|
// This is a generic function. V will generate it for every type it's used with.
|
||
|
fn (r Repo<T>) find_by_id(id int) ?T {
|
||
|
table_name := T.name // in this example getting the name of the type gives us the table name
|
||
|
return r.db.query_one<T>('select * from $table_name where id = ?', id)
|
||
|
}
|
||
|
|
||
|
db := new_db()
|
||
|
users_repo := new_repo<User>(db)
|
||
|
posts_repo := new_repo<Post>(db)
|
||
|
user := users_repo.find_by_id(1)?
|
||
|
post := posts_repo.find_by_id(1)?
|
||
|
```
|
||
|
|
||
|
## Concurrency
|
||
|
|
||
|
The concurrency model is very similar to Go. To run `foo()` concurrently, just
|
||
|
call it with `go foo()`. Right now, it launches the function in a new system
|
||
|
thread. Soon coroutines and the scheduler will be implemented.
|
||
|
|
||
|
## Decoding JSON
|
||
|
|
||
|
```v
|
||
|
import json
|
||
|
|
||
|
struct User {
|
||
|
name string
|
||
|
age int
|
||
|
|
||
|
// Use the `skip` attribute to skip certain fields
|
||
|
foo Foo [skip]
|
||
|
|
||
|
// If the field name is different in JSON, it can be specified
|
||
|
last_name string [json:lastName]
|
||
|
}
|
||
|
|
||
|
data := '{ "name": "Frodo", "lastName": "Baggins", "age": 25 }'
|
||
|
user := json.decode(User, data) or {
|
||
|
eprintln('Failed to decode json')
|
||
|
return
|
||
|
}
|
||
|
println(user.name)
|
||
|
println(user.last_name)
|
||
|
println(user.age)
|
||
|
```
|
||
|
|
||
|
JSON is very popular nowadays, that's why JSON support is built in.
|
||
|
|
||
|
The first argument of the `json.decode` function is the type to decode to.
|
||
|
The second argument is the JSON string.
|
||
|
|
||
|
V generates code for JSON encoding and decoding. No runtime reflection is used. This results in much better
|
||
|
performance.
|
||
|
|
||
|
## Testing
|
||
|
|
||
|
```v
|
||
|
// hello.v
|
||
|
fn hello() string {
|
||
|
return 'Hello world'
|
||
|
}
|
||
|
|
||
|
// hello_test.v
|
||
|
fn test_hello() {
|
||
|
assert hello() == 'Hello world'
|
||
|
}
|
||
|
```
|
||
|
|
||
|
All test functions have to be placed in `*_test.v` files and begin with `test_`.
|
||
|
|
||
|
To run the tests do `v hello_test.v`. To test an entire module, do
|
||
|
`v test mymodule`.
|
||
|
|
||
|
`assert` keyword can be used outside of tests as well.
|
||
|
|
||
|
## Memory management
|
||
|
|
||
|
(Work in progress)
|
||
|
There's no garbage collection or reference counting. V cleans everything up
|
||
|
during compilation. If your V program compiles, it's guaranteed that it's going
|
||
|
to be leak free. For example:
|
||
|
|
||
|
```v
|
||
|
fn draw_text(s string, x, y int) {
|
||
|
...
|
||
|
}
|
||
|
|
||
|
fn draw_scene() {
|
||
|
...
|
||
|
draw_text('hello $name1', 10, 10)
|
||
|
draw_text('hello $name2', 100, 10)
|
||
|
draw_text(strings.repeat('X', 10000), 10, 50)
|
||
|
...
|
||
|
}
|
||
|
```
|
||
|
|
||
|
The strings don't escape `draw_text`, so they are cleaned up when
|
||
|
the function exits.
|
||
|
|
||
|
In fact, the first two calls won't result in any allocations at all.
|
||
|
These two strings are small,
|
||
|
V will use a preallocated buffer for them.
|
||
|
|
||
|
```v
|
||
|
fn test() []int {
|
||
|
number := 7 // stack variable
|
||
|
user := User{} // struct allocated on stack
|
||
|
numbers := [1, 2, 3] // array allocated on heap, will be freed as the function exits
|
||
|
println(number)
|
||
|
println(user)
|
||
|
println(numbers)
|
||
|
numbers2 := [4, 5, 6] // array that's being returned, won't be freed here
|
||
|
return numbers2
|
||
|
}
|
||
|
```
|
||
|
|
||
|
## Defer
|
||
|
|
||
|
A defer statement defers the execution of a block of statements until the surrounding function returns.
|
||
|
|
||
|
```v
|
||
|
fn read_log() {
|
||
|
f := os.open('log.txt')
|
||
|
defer { f.close() }
|
||
|
...
|
||
|
if !ok {
|
||
|
// defer statement will be called here, the file will be closed
|
||
|
return
|
||
|
}
|
||
|
...
|
||
|
// defer statement will be called here, the file will be closed
|
||
|
}
|
||
|
```
|
||
|
|
||
|
## ORM
|
||
|
|
||
|
(alpha)
|
||
|
|
||
|
V has a built-in ORM that supports Postgres, and will soon support MySQL and SQLite.
|
||
|
|
||
|
The benefits of V ORM:
|
||
|
|
||
|
- One syntax for all SQL dialects. Migrating to a different database becomes much easier.
|
||
|
- Queries are constructed with V syntax. There's no need to learn another syntax.
|
||
|
- Safety. It's impossible to construct a SQL query with an injection.
|
||
|
- Compile time checks. No more typos that can only be caught at runtime.
|
||
|
- Readability and simplicity. You don't need to manually parse the results and construct objects.
|
||
|
|
||
|
```v
|
||
|
struct Customer { // struct name has to be the same as the table name for now
|
||
|
id int // an integer id must be the first field
|
||
|
name string
|
||
|
nr_orders int
|
||
|
country string
|
||
|
}
|
||
|
|
||
|
db := pg.connect(db_name, db_user)
|
||
|
|
||
|
// select count(*) from Customer
|
||
|
nr_customers := db.select count from Customer
|
||
|
println('number of all customers: $nr_customers')
|
||
|
|
||
|
// V syntax can be used to build queries
|
||
|
// db.select returns an array
|
||
|
uk_customers := db.select from Customer where country == 'uk' && nr_orders > 0
|
||
|
println(uk_customers.len)
|
||
|
for customer in uk_customers {
|
||
|
println('$customer.id - $customer.name')
|
||
|
}
|
||
|
|
||
|
// by adding `limit 1` we tell V that there will be only one object
|
||
|
customer := db.select from Customer where id == 1 limit 1
|
||
|
println('$customer.id - $customer.name')
|
||
|
|
||
|
// insert a new customer
|
||
|
new_customer := Customer{name: 'Bob', nr_orders: 10}
|
||
|
db.insert(new_customer)
|
||
|
```
|
||
|
|
||
|
## vfmt
|
||
|
|
||
|
You don't need to worry about formatting your code or style guidelines.
|
||
|
vfmt takes care of that:
|
||
|
|
||
|
```v
|
||
|
v fmt file.v
|
||
|
```
|
||
|
|
||
|
It's recommended to set up your editor, so that vfmt runs on every save.
|
||
|
|
||
|
Always run vfmt before pushing your code.
|
||
|
|
||
|
## writing_documentation
|
||
|
|
||
|
The way it works is very similar to Go. It's very simple: there's no need to
|
||
|
write documentation for your code, vdoc will generate it from the source code.
|
||
|
|
||
|
Documentation for each function/type/const must be placed right before the declaration:
|
||
|
|
||
|
```v
|
||
|
// clearall clears all bits in the array
|
||
|
fn clearall() {
|
||
|
|
||
|
}
|
||
|
```
|
||
|
|
||
|
The comment must start with the name of the definition.
|
||
|
|
||
|
An overview of the module must be placed in the first comment right after the module's name.
|
||
|
|
||
|
To generate documentation, run `v doc path/to/module` (TODO this is
|
||
|
temporarily disabled).
|
||
|
|
||
|
## Advanced Topics
|
||
|
|
||
|
## Calling C functions from V
|
||
|
|
||
|
```v
|
||
|
#flag -lsqlite3
|
||
|
#include "sqlite3.h"
|
||
|
|
||
|
struct C.sqlite3
|
||
|
struct C.sqlite3_stmt
|
||
|
|
||
|
fn C.sqlite3_column_int(stmt C.sqlite3_stmt, n int) int
|
||
|
|
||
|
fn main() {
|
||
|
path := 'users.db'
|
||
|
db := &C.sqlite3{!} // a temporary hack meaning `sqlite3* db = 0`
|
||
|
C.sqlite3_open(path.str, &db)
|
||
|
query := 'select count(*) from users'
|
||
|
stmt := &C.sqlite3_stmt{!}
|
||
|
C.sqlite3_prepare_v2(db, query.str, - 1, &stmt, 0)
|
||
|
C.sqlite3_step(stmt)
|
||
|
nr_users := C.sqlite3_column_int(stmt, 0)
|
||
|
C.sqlite3_finalize(stmt)
|
||
|
println(nr_users)
|
||
|
}
|
||
|
```
|
||
|
|
||
|
Add `#flag` directives to the top of your V files to provide C compilation flags like `-l` for
|
||
|
linking, `-I` for adding include files locations, `-D` for setting compile time variables, etc.
|
||
|
|
||
|
You can use different flags for different targets. Right now, `linux`, `darwin` , and `windows` are supported.
|
||
|
|
||
|
For now you have to use one flag per line:
|
||
|
|
||
|
```v
|
||
|
#flag linux -lsdl2
|
||
|
#flag linux -Ivig
|
||
|
#flag linux -DCIMGUI_DEFINE_ENUMS_AND_STRUCTS=1
|
||
|
#flag linux -DIMGUI_DISABLE_OBSOLETE_FUNCTIONS=1
|
||
|
#flag linux -DIMGUI_IMPL_API=
|
||
|
```
|
||
|
|
||
|
C strings can be converted to V strings with `string(cstring)` or `string(cstring, len)`.
|
||
|
|
||
|
V uses `voidptr` for C's `void*` and `byteptr` for C's `byte*` or `char*`.
|
||
|
|
||
|
To cast `voidptr` to V references use `user := &User(user_void_ptr)`.
|
||
|
|
||
|
`voidptr` can also be dereferenced to V structs by casting: `user := User(user_void_ptr)`.
|
||
|
|
||
|
Check out socket.v for an example of calling C code from V:
|
||
|
[https://github.com/vlang/v/blob/master/vlib/net/socket.v](https://github.com/vlang/v/blob/master/vlib/net/socket.v)
|
||
|
|
||
|
To debug issues with the C code, `v -show_c_cmd .` is useful. It prints the
|
||
|
C command that is used to build the program.
|
||
|
|
||
|
## Compile time if
|
||
|
|
||
|
```v
|
||
|
$if windows {
|
||
|
println('Windows')
|
||
|
}
|
||
|
$if linux {
|
||
|
println('Linux')
|
||
|
}
|
||
|
$if mac {
|
||
|
println('macOS')
|
||
|
}
|
||
|
|
||
|
$if debug {
|
||
|
println('debugging')
|
||
|
}
|
||
|
```
|
||
|
|
||
|
Compile time `if` starts with a `$`. Right now it can only be used to detect
|
||
|
an OS or a `-debug` compilation option.
|
||
|
|
||
|
## Reflection via codegen
|
||
|
|
||
|
Having built-in JSON support is nice, but V also allows you to create efficient
|
||
|
serializers for anything:
|
||
|
|
||
|
```v
|
||
|
// TODO: not implemented yet
|
||
|
fn decode<T>(data string) T {
|
||
|
mut result := T{}
|
||
|
for field in T.fields {
|
||
|
if field.typ == 'string' {
|
||
|
result.$field = get_string(data, field.name)
|
||
|
} else if field.typ == 'int' {
|
||
|
result.$field = get_int(data, field.name)
|
||
|
}
|
||
|
}
|
||
|
return result
|
||
|
}
|
||
|
|
||
|
// generates to:
|
||
|
fn decode_User(data string) User {
|
||
|
mut result := User{}
|
||
|
result.name = get_string(data, 'name')
|
||
|
result.age = get_int(data, 'age')
|
||
|
return result
|
||
|
}
|
||
|
```
|
||
|
|
||
|
## Limited operator overloading
|
||
|
|
||
|
```v
|
||
|
struct Vec {
|
||
|
x int
|
||
|
y int
|
||
|
}
|
||
|
|
||
|
fn (a Vec) str() string {
|
||
|
return '{$a.x, $a.y}'
|
||
|
}
|
||
|
|
||
|
fn (a Vec) + (b Vec) Vec {
|
||
|
return Vec {
|
||
|
a.x + b.x,
|
||
|
a.y + b.y
|
||
|
}
|
||
|
}
|
||
|
|
||
|
fn (a Vec) - (b Vec) Vec {
|
||
|
return Vec {
|
||
|
a.x - b.x,
|
||
|
a.y - b.y
|
||
|
}
|
||
|
}
|
||
|
|
||
|
fn main() {
|
||
|
a := Vec{2, 3}
|
||
|
b := Vec{4, 5}
|
||
|
println(a + b) // "{6, 8}"
|
||
|
println(a - b) // "{-2, -2}"
|
||
|
}
|
||
|
```
|
||
|
|
||
|
Operator overloading goes against V's philosophy of simplicity and predictability. But since
|
||
|
scientific and graphical applications are among V's domains, operator overloading is very important to have
|
||
|
in order to improve readability:
|
||
|
|
||
|
`a.add(b).add(c.mul(d))` is a lot less readable than `a + b + c * d`.
|
||
|
|
||
|
To improve safety and maintainability, operator overloading has several limitations:
|
||
|
|
||
|
-It's only possible to overload `+, -, *, /` operators.
|
||
|
|
||
|
- Calling other functions inside operator functions is not allowed.
|
||
|
|
||
|
- Operator functions can't modify their arguments.
|
||
|
|
||
|
- Both arguments must have the same type (just like with all operators in V).
|
||
|
|
||
|
## Inline assembly
|
||
|
|
||
|
TODO: not implemented yet
|
||
|
|
||
|
```v
|
||
|
fn main() {
|
||
|
a := 10
|
||
|
asm x64 {
|
||
|
mov eax, [a]
|
||
|
add eax, 10
|
||
|
mov [a], eax
|
||
|
}
|
||
|
}
|
||
|
```
|
||
|
|
||
|
## Translating C/C++ to V
|
||
|
|
||
|
TODO: translating C to V will be available in V 0.3. C++ to V will be available later this year.
|
||
|
|
||
|
V can translate your C/C++ code to human readable V code.
|
||
|
Let's create a simple program `test.cpp` first:
|
||
|
|
||
|
```v
|
||
|
#include <vector>
|
||
|
#include <string>
|
||
|
#include <iostream>
|
||
|
|
||
|
int main() {
|
||
|
std::vector<std::string> s;
|
||
|
s.push_back("V is ");
|
||
|
s.push_back("awesome");
|
||
|
std::cout << s.size() << std::endl;
|
||
|
return 0;
|
||
|
}
|
||
|
```
|
||
|
|
||
|
Run `v translate test.cpp` and V will generate `test.v`:
|
||
|
|
||
|
```v
|
||
|
fn main {
|
||
|
mut s := []
|
||
|
s << 'V is '
|
||
|
s << 'awesome'
|
||
|
println(s.len)
|
||
|
}
|
||
|
```
|
||
|
|
||
|
An online C/C++ to V translator is coming soon.
|
||
|
|
||
|
When should you translate C code and when should you simply call C code from V?
|
||
|
|
||
|
If you have well-written, well-tested C code, then of course you can always simply call this C code from V.
|
||
|
|
||
|
Translating it to V gives you several advantages:
|
||
|
|
||
|
- If you plan to develop that code base, you now have everything in one language, which is much safer and easier to develop in than C.
|
||
|
|
||
|
- Cross-compilation becomes a lot easier. You don't have to worry about it at all.
|
||
|
|
||
|
- No more build flags and include files either.
|
||
|
|
||
|
## Hot code reloading
|
||
|
|
||
|
```v
|
||
|
module main
|
||
|
|
||
|
import time
|
||
|
import os
|
||
|
|
||
|
[live]
|
||
|
fn print_message() {
|
||
|
println('Hello! Modify this message while the program is running.')
|
||
|
}
|
||
|
|
||
|
fn main() {
|
||
|
for {
|
||
|
print_message()
|
||
|
time.sleep_ms(500)
|
||
|
}
|
||
|
}
|
||
|
|
||
|
```
|
||
|
|
||
|
Build this example with `v -live message.v`.
|
||
|
|
||
|
Functions that you want to be reloaded must have `[live]` attribute
|
||
|
before their definition.
|
||
|
|
||
|
Right now it's not possible to modify types while the program is running.
|
||
|
|
||
|
More examples, including a graphical application:
|
||
|
[github.com/vlang/v/tree/master/examples/hot_code_reloading](https://github.com/vlang/v/tree/master/examples/hot_code_reloading).
|
||
|
|
||
|
## Cross compilation
|
||
|
|
||
|
To cross compile your project simply run
|
||
|
|
||
|
```v
|
||
|
v -os windows .
|
||
|
```
|
||
|
|
||
|
or
|
||
|
|
||
|
```v
|
||
|
v -os linux .
|
||
|
```
|
||
|
|
||
|
(Cross compiling for macOS is temporarily not possible.)
|
||
|
|
||
|
If you don't have any C dependencies, that's all you need to do. This works even
|
||
|
when compiling GUI apps using the `ui` module or graphical apps using `gg`.
|
||
|
|
||
|
You will need to install Clang, LLD linker, and download a zip file with
|
||
|
libraries and include files for Windows and Linux. V will provide you with a link.
|
||
|
|
||
|
## Cross-platform shell scripts in V
|
||
|
|
||
|
V can be used as an alternative to Bash to write deployment scripts, build scripts, etc.
|
||
|
|
||
|
The advantage of using V for this is the simplicity and predictability of the language, and
|
||
|
cross-platform support. "V scripts" run on Unix-like systems as well as on Windows.
|
||
|
|
||
|
Use .vsh file extension. It will make all functions in the `os`
|
||
|
module global (so that you can use `ls()` instead of `os.ls()`, for example).
|
||
|
|
||
|
```v
|
||
|
rm('build/*')
|
||
|
// Same as:
|
||
|
for file in ls('build/') {
|
||
|
rm(file)
|
||
|
}
|
||
|
|
||
|
mv('*.v', 'build/')
|
||
|
// Same as:
|
||
|
for file in ls('.') {
|
||
|
if file.ends_with('.v') {
|
||
|
mv(file, 'build/')
|
||
|
}
|
||
|
}
|
||
|
```
|
||
|
|
||
|
Now you can either compile this like a normal V program and get an executable you can deploy and run
|
||
|
anywhere:
|
||
|
`v deploy.v && ./deploy`
|
||
|
|
||
|
Or just run it more like a traditional bash script:
|
||
|
`v run deploy.v`
|
||
|
|
||
|
## Appendix I: Keywords
|
||
|
|
||
|
V has 23 keywords:
|
||
|
|
||
|
```v
|
||
|
break
|
||
|
const
|
||
|
continue
|
||
|
defer
|
||
|
else
|
||
|
enum
|
||
|
fn
|
||
|
for
|
||
|
go
|
||
|
goto
|
||
|
if
|
||
|
import
|
||
|
in
|
||
|
interface
|
||
|
match
|
||
|
module
|
||
|
mut
|
||
|
none
|
||
|
or
|
||
|
pub
|
||
|
return
|
||
|
struct
|
||
|
type
|
||
|
```
|
||
|
|
||
|
## Appendix II: Operators
|
||
|
|
||
|
```v
|
||
|
+ sum integers, floats, strings
|
||
|
- difference integers, floats
|
||
|
* product integers, floats
|
||
|
/ quotient integers, floats
|
||
|
% remainder integers
|
||
|
|
||
|
& bitwise AND integers
|
||
|
| bitwise OR integers
|
||
|
^ bitwise XOR integers
|
||
|
|
||
|
<< left shift integer << unsigned integer
|
||
|
>> right shift integer >> unsigned integer
|
||
|
|
||
|
|
||
|
Precedence Operator
|
||
|
5 * / % << >> &
|
||
|
4 + - | ^
|
||
|
3 == != < <= > >=
|
||
|
2 &&
|
||
|
1 ||
|
||
|
|
||
|
|
||
|
Assignment Operators
|
||
|
+= -= *= /= %=
|
||
|
&= |= ^=
|
||
|
>>= <<=
|
||
|
```
|