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 enrolledenrolled_status method (below) has a receiver of type {{code|1=Client}} named {{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">

<syntaxhighlight lang="V">

struct Client {

enrolled bool

age int

}

fn (x Client) enrolledenrolled_status() bool {

return x.age > 12enrolled

}

println(client_2.Client{enrolled: true}.enrolled_status()) // "true"

client_1 := Client{

println(client_1.Client{enrolled: false}.enrolled_status()) // "false"

age: 8

}

client_2 := Client{

age: 30

}

println(client_1.enrolled()) // "false"

println(client_2.enrolled()) // "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==