Macro sketchbook::compose

macro_rules! compose {
    {
        $(#[$($meta_code:tt)*])?
        $v:vis struct $name:ident {
            $(
                $(#[$attr:ident])? $vi:vis $field:ident: $field_type:ty
            ),*$(,)?
        }
    } => { ... };
    {
        $(#[$($meta_code:tt)*])?
        $v:vis enum $name:ident {
            $($(#[$attr:ident])? $variant:ident$(($variant_type:ty))?),*$(,)?
        }
    } => { ... };
}

Create type composed of other types.

For structs, this macro is used in the following way. When the #[part] attribute is applied to a field, that field will be available using AsPart<T>. Only one field can have a #[part] of a particular type.

compose! {
    struct Test {
        a: i32,
         
        #[part]
        b: i32,
                   
        #[part]
        c: f32,
    }
}

let x = Test { a: 123, b: 456, c: 1.23 };
let y: &f32 = x.as_part();
assert_eq!(y, &1.23);

For enums, this macro is used in the following way. When the #[part] attribute is applied to a variant, that variant will be available using TryAsPart<T>. Only one variant can have a #[part] of a particular type. Additionally, the variant must be a tuple of a single value.

compose! {
    enum Test {
        A,
         
        #[part]
        B(i32),
                                            
        #[part]
        C(f32),
    }
}
                                            
let x = Test::B(123);
let y: Option<&i32> = x.try_as_part();
assert_eq!(y, Some(&123));