Trait frunk::hlist::HFoldLeftable

pub trait HFoldLeftable<Folder, Acc> {
    type Output;
    fn foldl(self, folder: Folder, acc: Acc) -> Self::Output;
}

Trait for performing a left fold over an HList

This trait is part of the implementation of the inherent method HCons::foldl. Please see that method for more information.

You only need to import this trait when working with generic HLists or Mappers of unknown type. If the type of everything is known, then list.foldl(f, acc) should "just work" even without the trait.

Associated Types

type Output

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Required methods

fn foldl(self, folder: Folder, acc: Acc) -> Self::Output

Perform a left fold over an HList.

Please see the inherent method for more information.

The only difference between that inherent method and this trait method is the location of the type parameters. (here, they are on the trait rather than the method)

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Implementors

impl<F, Acc> HFoldLeftable<F, Acc> for HNil

type Output = Acc

fn foldl(self, F, acc: Acc) -> <HNil as HFoldLeftable<F, Acc>>::Output

impl<F, H, Tail, Acc> HFoldLeftable<F, Acc> for HCons<H, Tail> where
    F: Fn(Acc, H) -> Acc,
    Tail: HFoldLeftable<F, Acc>, 

Implementation for folding over an HList using a single function that can handle all cases

let h = hlist![1, 2, 3, 4, 5];

let r: isize = h.foldl(|acc, next| acc + next, 0);
assert_eq!(r, 15);

type Output = <Tail as HFoldLeftable<F, Acc>>::Output

fn foldl(
    self,
    f: F,
    acc: Acc
) -> <HCons<H, Tail> as HFoldLeftable<F, Acc>>::Output

impl<F, R, FTail, H, Tail, Acc> HFoldLeftable<HCons<F, FTail>, Acc> for HCons<H, Tail> where
    F: FnOnce(Acc, H) -> R,
    Tail: HFoldLeftable<FTail, R>, 

type Output = <Tail as HFoldLeftable<FTail, R>>::Output

fn foldl(
    self,
    folder: HCons<F, FTail>,
    acc: Acc
) -> <HCons<H, Tail> as HFoldLeftable<HCons<F, FTail>, Acc>>::Output

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