Struct

struct statement declares a new struct.

Specifications

A struct is a custom data type that groups related values together as fields. Each field is declared with var and must have a default value.

To create a new instance of a struct, call it like a function with no arguments, such as Foo(). This creates a new instance with all fields set to their default values.

Fields and instance functions can be accessed with ., such as instance.field or instance.method().

Static functions belong to the type itself rather than instance, and can be called as Foo.method().

If you would like to create struct instances with non-default values, define the functions using static just like Foo.new().

For more information about struct fields and member functions, visit the struct field page and function page.

Syntax

struct <Struct Name> {
    // Struct Field
    var <Field> = <Default Value>
    
    // Instance Function
    func <Method>() { }
    
    // Static Function
    static func <Method>() { }
}

Example 1 --- Basic

This example program declares a struct called Point and initializes it using Point().

struct Point {
    var x = 0.0
    var y = 0.0
}

func main() {
    var p = Point()
    p.x = 3.0
    p.y = 4.0
}

Example 2 --- Member Functions

The program below creates a struct called Circle which has a static function to initialize a new circle with the given radius and a instance function that scales the circle by the given factor.

import std

struct Circle {
    var radius = 0.0

    static func new(radius r: Float) -> Circle {
        var c = Circle()
        c.radius = r
        return c
    }

    func scale(factor: Float) {
        self.radius = self.radius * factor
    }
}

func main() {
    var c = Circle.new(radius: 5.0)
    c.scale(2.0)
}