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v/vlib/compiler/match.v

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// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module compiler
import (
strings
)
// Returns typ if used as expression
fn (p mut Parser) match_statement(is_expr bool) string {
p.check(.key_match)
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p.fspace()
p.cgen.start_tmp()
typ := p.bool_expression()
if typ.starts_with('array_') {
p.error('arrays cannot be compared')
}
expr := p.cgen.end_tmp()
// is it safe to use p.cgen.insert_before ???
tmp_var := p.get_tmp()
p.cgen.insert_before('$typ $tmp_var = $expr;')
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p.fspace()
p.check(.lcbr)
mut i := 0
mut all_cases_return := true
// stores typ of resulting variable
mut res_typ := ''
defer {
p.check(.rcbr)
}
for p.tok != .rcbr {
if p.tok == .key_else {
p.check(.key_else)
if p.tok == .arrow {
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p.error(warn_match_arrow)
}
// unwrap match if there is only else
if i == 0 {
if is_expr {
// statements are dissallowed (if match is expression) so user cant declare variables there and so on
// allow braces is else
got_brace := p.tok == .lcbr
if got_brace {
p.check(.lcbr)
}
p.gen('( ')
res_typ = p.bool_expression()
p.gen(' )')
// allow braces in else
if got_brace {
p.check(.rcbr)
}
return res_typ
} else {
p.returns = false
p.check(.lcbr)
p.genln('{ ')
p.statements()
p.returns = all_cases_return && p.returns
return ''
}
}
if is_expr {
// statements are dissallowed (if match is expression) so user cant declare variables there and so on
p.gen(':(')
// allow braces is else
got_brace := p.tok == .lcbr
if got_brace {
p.check(.lcbr)
}
p.check_types(p.bool_expression(), res_typ)
// allow braces in else
if got_brace {
p.check(.rcbr)
}
p.gen(strings.repeat(`)`, i+1))
return res_typ
} else {
p.returns = false
p.genln('else // default:')
p.check(.lcbr)
p.genln('{ ')
p.statements()
p.returns = all_cases_return && p.returns
return ''
}
}
if i > 0 {
if is_expr {
p.gen(': (')
} else {
p.gen('else ')
}
} else if is_expr {
p.gen('(')
}
if is_expr {
p.gen('(')
} else {
p.gen('if (')
}
ph := p.cgen.add_placeholder()
// Multiple checks separated by comma
mut got_comma := false
for {
if got_comma {
p.gen(') || (')
}
mut got_string := false
if typ == 'string' {
got_string = true
p.gen('string_eq($tmp_var, ')
}
else {
p.gen('$tmp_var == ')
}
p.expected_type = typ
p.check_types(p.bool_expression(), typ)
p.expected_type = ''
if got_string {
p.gen(')')
}
if p.tok != .comma {
if got_comma {
p.gen(') ')
p.cgen.set_placeholder(ph, '(')
}
break
}
p.check(.comma)
got_comma = true
}
p.gen(')')
if p.tok == .arrow {
p.warn(warn_match_arrow)
p.check(.arrow)
}
// statements are dissallowed (if match is expression) so user cant declare variables there and so on
if is_expr {
p.gen('? (')
// braces are required for now
p.check(.lcbr)
if i == 0 {
// on the first iteration we set value of res_typ
res_typ = p.bool_expression()
} else {
// later on we check that the value is of res_typ type
p.check_types(p.bool_expression(), res_typ)
}
// braces are required for now
p.check(.rcbr)
p.gen(')')
}
else {
p.returns = false
p.check(.lcbr)
p.genln('{ ')
p.statements()
all_cases_return = all_cases_return && p.returns
// p.gen(')')
}
i++
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p.fgenln('')
}
if is_expr {
// we get here if no else found, ternary requires "else" branch
p.error('Match expression requires "else"')
}
p.returns = false // only get here when no default, so return is not guaranteed
return ''
}
fn (p mut Parser) switch_statement() {
p.error('`switch` statement has been removed, use `match` instead:\n' +
'https://vlang.io/docs#match')
}