Macro destructure 

macro_rules! destructure {
    (let $S:path { $($field_spec:tt)* } = $value:expr) => { ... };
    (let ($($var:pat_param),* $(,)?) = $value:expr) => { ... };
}

Allows destructuring in const contexts.

Examples

Destructuring tuples:

use const_tools::destructure;

const fn swap<A, B>(value: (A, B)) -> (B, A) {
    destructure!(let (a, b) = value);
    (b, a)
}

Destructuring structs:

use const_tools::destructure;

struct Pair<A, B> {
    first: A,
    second: B,
}

impl<A, B> Pair<A, B> {
    const fn swap(self) -> Pair<B, A> {
        destructure!(let Self { first, second } = self);
        Pair { first: second, second: first }
    }
}