The Mun Programming Language

Struct Memory Kind

By default, Mun is a garbage collected language. This means that memory is allocated on the heap and automatically freed by the Mun Runtime when your memory goes out of scope. Sometimes this behavior is undesired, and you want to manually control when a value is freed.

Mun allows you to specify this so-called memory kind in a struct definition: gc for garbage collection or value to pass a struct by value; defaulting to gc when neither is specified. Listing 4-9 shows the previously created struct definition of a Vector2, which has the default gc memory kind.

pub struct Vector2 {
    x: f32,
    y: f32,
}

Listing 4-9: A record struct definition for a 2D vector, defaulting to the gc memory kind

To manually specify the memory kind, add round brackets containing either gc or value after the struct keyword, as illustrated in Listing 4-10.

pub struct(value) Vector2 {
    x: f32,
    y: f32,
}

Listing 4-10: A record struct definition for a 2D vector, with the value memory kind