Merge Merge/MergeBy/MergeJoinBy implementations
#711
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To get rid of `const SAME: bool`, I wrap the function `F` in `MergeFuncLR` and `MergeFuncT`. Those `MergeFuncLR/T` have a parameter `T` (phantom field) to not have conflicting implementations of `MergePredicate<L, R>`. In `merge_join_by` definition, in order for the compiler to keep guessing left/right types, I kept `F: FnMut(&Self::Item, &J::Item) -> T`. But to not add `F: MergePredicate<Self::Item, J::Item>` that felt duplicate, I removed `T: OrderingOrBool...`, the user might lose `OrderingOrBool` information.
And I simplify `MergeFuncLR` and `MergeFuncT` to "tuple structs".
Basically because `PutBack<Fuse<I>>` is fused no matter if `I` is or not. Same for `J`.
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Hi @Philippe-Cholet, thanks for this. I try to pick this up, but I am very unsure that |
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@phimuemue A bit disappointed, I started again and to my own surprise I quickly found a way (fresh eyes I guess). So 0a3f122 |
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I'm closing this. This is the result of some useful experiments but became too messy to be properly reviewed and it deserves a cleaner PR I'm currently working on. |
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MergeandMergeByare moved from "adaptors" to "merge_join" modules.Then
Merge,MergeByandMergeJoinByare now instances of a new (common and private) struct:InternalMergeJoinBy.Internally, instead of
OrderingOrBoolandFnMut(&L, &R) -> Out, we useMergePredicate<L, R, Out=...>(OutbeingOrderingorbool).And with
MergeFuncTandMergeFuncLRalso kept private, the functions return those types:The only changes for an external user:
MergeJoinBysadly requires now a fourth type (it was that or share the internalMergeFuncLRpublicly).MergeJoinBynow implementsFusedIteratortoo.Closes #701
PS: In
fn merge_join_by, the constraintT: OrderingOrBool<I::Item, J::Item>,has been removed. Even if the documentation is clear, we could add it back in some way if you want.