Macro v9::decl_property

macro_rules! decl_property {
    (
        $(#[$meta:meta])*
        $vis:vis $name:ident
            $(: $local_type:ty)?
            $(: ~$nonlocal_type:ty)?
    ) => { ... };
    (
        $(#[$meta:meta])*
        $vis:vis $name:ident
            $(: $local_type:ty)?
            $(: ~$nonlocal_type:ty)?
            = $init:expr;
    ) => { ... };
    (@if $ty:ty) => { ... };
    (@wrap_nonlocal ; $(#[$meta:meta])*) => { ... };
    (@wrap_nonlocal $nonlocal_type:ty; $(#[$meta:meta])*) => { ... };
}

Declares a singleton property.

Example

decl_property! {
    /// Documentation can go here.
    /// This property is initialized via `Default`.
    #[derive(Clone)] // Derives also.
    pub MY_PROPERTY: ~i32
}

decl_property! {
    // You can also initialize with an expression. Note the trailing semicolon.
    pub EXPLICIT_INIT: ~i32 = 237;
}

fn main() {
    let mut universe = Universe::new();
    MY_PROPERTY::register(&mut universe);
    EXPLICIT_INIT::register(&mut universe);
    universe.kmap(|a: &mut MY_PROPERTY, b: &EXPLICIT_INIT| {
        **a += **b;
    });
}

impl doesn't use types inside crate

This is an error you’ll get if you try to make a property out of a type you don’t own. You can get around this by putting a ~ in front of the type, as is done in the example here. They’ll be slightly less pleasant to use… as you can see in the example here.