Crate type_const

Expand description

This crate provides simple utils for passing const values around through generics, in the form of types.

The concept of a type const is expressed through the Const trait, which holds the type and the value of the constant.

Passing values that are known at compile time through generics is different from passing them through arguments, for example:

const fn array_of_const<C: type_const::Const, const N: usize>() -> [C::Type; N] {
    [C::VALUE; N] // no `Copy` needed!
}
assert_eq!(array_of_const::<type_const::DefaultOf<i32>, 3>(), [0; 3]);

This may also be used to write const “functions” in traits without the nightly const_trait feature. Note that unlike const fn, these can only be evaluated at compile time.

trait AddConst<Rhs=Self> {
    type Output;
    type Add<
        LhsC: type_const::Const<Type = Self>,
        RhsC: type_const::Const<Type = Rhs>,
    >: type_const::Const<Type = Self::Output>;
}

Modules§

consts: A small collection of useful consts.

Structs§

DefaultOf: A Const that evaluates to DefaultConst::DEFAULT.

Traits§

Const: Describes a type that holds an associated const value.
DefaultConst: A const version of Default.

Functions§

value_of: Alias for Const::VALUE. Prefer this function over accessing the const directly.

Type Aliases§