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Prevent exponentially large type sizes in tuple_combinations #945

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May 24, 2024
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Prevent exponentially large type sizes in tuple_combinations #945

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16 changes: 14 additions & 2 deletions src/adaptors/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -773,16 +773,28 @@ macro_rules! impl_tuple_combination {
where
F: FnMut(B, Self::Item) -> B,
{
// We outline this closure to prevent it from unnecessarily
// capturing the type parameters `I`, `B`, and `F`. Not doing
// so ended up causing exponentially big types during MIR
// inlining when building itertools with optimizations enabled.
//
// This change causes a small improvement to compile times in
// release mode.
type CurrTuple<A> = (A, $(ignore_ident!($X, A)),*);
type PrevTuple<A> = ($(ignore_ident!($X, A),)*);
fn map_fn<A: Clone>(z: &A) -> impl FnMut(PrevTuple<A>) -> CurrTuple<A> + '_ {
move |($($X,)*)| (z.clone(), $($X),*)
}
let Self { c, item, mut iter } = self;
if let Some(z) = item.as_ref() {
init = c
.map(|($($X,)*)| (z.clone(), $($X),*))
.map(map_fn::<A>(z))
.fold(init, &mut f);
}
while let Some(z) = iter.next() {
let c: $P<I> = iter.clone().into();
init = c
.map(|($($X,)*)| (z.clone(), $($X),*))
.map(map_fn::<A>(&z))
.fold(init, &mut f);
}
init
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