precompile is a nightly-only crate that uses #![feature(specialization)]
for precompiling specific monomorphizations of a generic function.
This can provide a benefit for generic functions that are expected to be used
with a limited set of types from multiple downstream crates.
For example:
// crate: A
pub fn generic_fn<T>() {
// ...
}
// crate B
A::generic_fn::<u32>();
// crate C
A::generic_fn::<u32>();This code will usually compile A::generic_fn::<u32> twice.
Whereas if we precompile generic_fn:
// crate: A
#[precompile::precompile]
#[precompile_with(u32)]
pub fn generic_fn<T>() {
// ...
}Then no matter how many crates use A::generic_fn::<u32>, it will only be
compiled once, when the crate A is built.
This means a possibly larger upfront compile-time cost for building A, in exchange for
a cheaper monomorphization cost when used downstream.