v/examples/generic_repository.v

// Please share your thoughts, suggestions, questions, etc here:
// https://github.com/vlang-io/V/issues/3

// I'm very interested in your feedback.

module main

struct User { /* ... */ }
struct Post { /* ... */ }
struct DB   { /* ... */ }

struct Repo <T> {
	db DB
}

// Generic code is notoriously verbose. To reduce clutter, V doesn't require you 
// to add `<T>` every time, since it already knows that Repo is a generic type.
fn new_repo<T>(db DB) Repo {
	return Repo<T>{db: db}
}

// This is a generic function. V will generate it for every type it's used with.
fn (r Repo) find_by_id(id int) T? { // `?` means the function returns an optional
	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)
}

fn main() {
	db := new_db()
	users_repo := new_repo<User>(db)
	// I'm also considering passing the type as an argument
	// users_repo := new_repo(User, db)
	posts_repo := new_repo<Post>(db)
	user := users_repo.find_by_id(1) or {
		eprintln('User not found')
		return
	}
	post := posts_repo.find_by_id(1) or {
		eprintln('Post not found')
		return
	}
}