V (programming language): Difference between revisions

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== Syntax ==

=== Hello world ===

The [["Hello, World!" program]] in V:<ref name="MUO"/><ref name=":0">{{Cite web |title=V Documentation |url=https://docs.vlang.io/ |access-date=2025-08-25 |website=docs.vlang.io}} {{Free-content attribution|title = V Documentation| license statement URL =https://github.com/vlang/v?tab=MIT-1-ov-file| license=The MIT License|this = yes}}</ref>

The [["Hello, World!" program]] in V:<ref name="MUO"/>

<syntaxhighlight lang="v">

fn main() {

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=== Variables ===

Variables are immutable by default and are defined using {{code|1=:=}} and a value. Use the {{code|mut}} [[reserved word]] (keyword) to make them mutable. Mutable variables can be assigned to using {{code|1==}}:{{sfn|Rao|2021|pp=28-40}}<ref name=":0" />

<syntaxhighlight lang="V">

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</syntaxhighlight>

Redeclaring a variable, whether in an inner scope or in the same scope, is not allowed:{{sfn|Rao|2021|pp=28-40}}<ref name=":0" />

<syntaxhighlight lang="V">

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=== Structs ===

Struct example:<ref name="Knott"/><ref name="section"/><ref name=":0" />

<syntaxhighlight lang="v">

struct FoobarFoo {

number int

name string

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// Struct fields can be initialized by name

var1 := FoobarFoo {

number: 21

name: "baz"

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// or by position

var2 := FoobarFoo{50, "quxtaz", 3.14}

</syntaxhighlight>

=== Heap structs ===

StructsBy thatdefault, structs are allocated on the stack. When structs are referenced by using the prefix {{code|1=&}} or have the heap attribute, willthey beare allocated toon the heap instead of the stack:{{sfn|Rao|2021}}<ref name=":0" />

<syntaxhighlight lang="v">

struct Foo {

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@[heap]

struct BarBaz {

number f32

}

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var1 := &Foo{2}

// BarBaz is always heap allocated because of its [heap] attribute

var2 := BarBaz{4.5}

</syntaxhighlight>

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[[Method (computer programming)|Methods]] in V are functions defined with a receiver [[Parameter (computer programming)|argument]]. The receiver appears in its own argument list between the fn keyword and the method name. Methods must be in the same [[Modular programming|module]] as the receiver type.

The is_registeredenrolled_status method (below) has a receiver of type User{{code|1=Client}} named u{{code|1=x}}. The convention is not to use receiver names like self or this, but preferably a short name. For example:<ref name="Knott"/><ref name="nasufi"/><ref name=":0" /><syntaxhighlight lang="v">

struct UserClient {

enrolled bool

{{Copyvio|timestamp=20250715164557 |url=https://docs.vlang.io/structs.html#methods}}

<syntaxhighlight lang="V">

struct User {

age int

}

fn (ux UserClient) is_registeredenrolled_status() bool {

return x.enrolled

return u.age > 16

}

println(Client{enrolled: true}.enrolled_status()) // true

user := User{

println(Client{enrolled: false}.enrolled_status()) // false

age: 10

}

println(user.is_registered()) // "false"

user2 := User{

age: 20

}

println(user2.is_registered()) // "true"

</syntaxhighlight>

</div>

=== Error handling ===

Result types may represent an error returned from a function. Result types are declared by prepending {{code|!}}: {{code|!Type}}

{{Copyvio|timestamp=20250715164557 |url=https://docs.vlang.io/type-declarations.html#optionresult-types-and-error-handling}}

Optional types are for types which may represent none. Result types may represent an error returned from a function.

OptionOptional types are declared bymay prependingrepresent {{code|?none}}. toOption thetypes type name:prepend {{code|?Type}}. Resultto typesthe usetype {{code|!}}name: {{code|!?Type}}.<ref name="Knott"/><ref name="section"/>{{Sfn|Tsoukalos|2022}}<ref name=":0" />

<syntaxhighlight lang="V">

fn something(t string) !string {

if t == "foo" { return "foo" }

return error("invalid string")

}

x := something("foo") or { "default" } // x will be "foo"

y := something("carbaz") or { "default" } // y will be "default"

z := something("carbaz") or { panic("{err}") } // z will exit with an error "invalid string" and a traceback

println(x)

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</syntaxhighlight>

</div>

==See also==