struct.md

Struct

A struct is a composite data type (or record) declaration that defines a physically grouped list of variables under one name in a block of memory, allowing different variables to be accessed via a single pointer or by the struct declared name which returns the same address.

For people coming from OOP languages, it can be thought as class but with more restrictions.

struct User {
    name string
    email string
    country string
}

fn main() {
	user := User {
			name: "V developers"
			email: "[email protected]"
			country: "Canada"
	}

	println(user.country)
}

Note: Structs are allocated on the stack.

You can use a comma to separate each field when creating a new instance of the struct. It's useful when you want to create a new instance on a single line.

user := User { name: "V developers", email: "[email protected]", country: "Canada" }

The & prefix

You can allocate a struct on the heap and get a reference to it by using the & prefix as follows:

user := &User{"V developers", "[email protected]", "Canada"}
println(user.name)

The type of user is &User. It's a reference to User.

Access modifiers

Struct fields are private and immutable by default. Their access modifiers can be changed with pub and mut.

struct User {
    email string
}

You can define them as private mutable.

struct User {
    email string
mut:
    first_name string
    last_name string
}

You can also define them as public immmutable (readonly).

struct User {
    email string
mut:
    first_name string
    last_name string
pub:
    sin_number int
}

or as public, but mutable only in the parent module.

struct User {
   email string
mut:
   first_name string
   last_name string
pub:
   sin_number int
pub mut:
   phone int
}

or public and mutable both inside and outside parent module.

struct User {
    email string
mut:
    first_name string
    last_name string
pub:
    sin_number int
pub mut:
    phone int
pub mut mut:
    address_1 string
    address_2 string
    city string
    country string
    zip     string
}

Exercises

1. Create a struct that stores and displays user information.
2. Create a Point struct that holds x and y field and guard them with private and public.