This is my current intended direction for what to propose in P2322 (the latest draft still uses fold_left and fold_right, but the next one will propose what I'm doing in this PR). There's a few more fold algorithms I intend to add to range-v3 but not std (like a short-circuiting fold and a fold that returns the iterator that it leaves off at), but the combinatorial explosion is a bit much, so I thought I'd start with this.
foldl is like accumulate except it doesn't take a default operation and can return a type other than the initial value (so that foldl([0.25, 0.75], 1, plus()) == 2.0).
foldl1 doesn't take an initial value, and instead returns an optional<U>. For instance, min(r) can be implemented as *foldl1(r, min).
foldr and foldr1 are the right-fold counterparts.
I like going with Haskell's names here because they're short, symmetric, and unambiguous. Some languages went the route of using fold (for the algorithm that takes an initial value) and reduce (for the algorithm that doesn't), Rust being the latest addition to that unfortunate club, and we can't do that even if we wanted to.
This is my current intended direction for what to propose in P2322 (the latest draft still uses
fold_leftandfold_right, but the next one will propose what I'm doing in this PR). There's a few more fold algorithms I intend to add to range-v3 but not std (like a short-circuiting fold and a fold that returns the iterator that it leaves off at), but the combinatorial explosion is a bit much, so I thought I'd start with this.foldlis likeaccumulateexcept it doesn't take a default operation and can return a type other than the initial value (so thatfoldl([0.25, 0.75], 1, plus()) == 2.0).foldl1doesn't take an initial value, and instead returns anoptional<U>. For instance,min(r)can be implemented as*foldl1(r, min).foldrandfoldr1are the right-fold counterparts.I like going with Haskell's names here because they're short, symmetric, and unambiguous. Some languages went the route of using
fold(for the algorithm that takes an initial value) andreduce(for the algorithm that doesn't), Rust being the latest addition to that unfortunate club, and we can't do that even if we wanted to.