Macro emplacable::unsize

macro_rules! unsize {
    ($e:expr, ($src:ty) -> $dst:ty) => { ... };
}

Helper for coercing values to unsized types.

The unsized_fn_params has some rough edges when it comes to coercing sized values to unsized ones by value. This macro works around that.

If you have a value val of type SizedType, and you want to coerce it to UnsizedType, write unsize!(val, (SizedType) -> UnsizedType)).

Probably useless without the unsized_fn_params or unsized_locals nightly features.

Requires the alloc crate feature (though doesn’t actually allocate on the heap).

Example

#![feature(unsized_fn_params)]

use core::fmt::Debug;

use emplacable::{box_new, unsize};

let mut my_box: Box<dyn Debug> = box_new(unsize!("hello world!", (&str) -> dyn Debug));

dbg!(&my_box);