Document unintuitive argument order for Vec::dedup_by relation #43041
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When trying to use dedup_by to merge some auxiliary information from removed elements into kept elements, I was surprised to observe that vec.dedup_by(same_bucket) calls same_bucket(a, b) where b appears before a in the vector, and discards a when true is returned. This argument order is probably a bug, but since it has already been stabilized, I guess we should document it as a feature and move on. (Vec::dedup also uses == with this unexpected argument order, but I figure that’s not important since == is expected to be symmetric with no side effects.) Signed-off-by: Anders Kaseorg <andersk@mit.edu>
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@bors: r+ |
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Mark-Simulacrum
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Document unintuitive argument order for Vec::dedup_by relation When trying to use `dedup_by` to merge some auxiliary information from removed elements into kept elements, I was surprised to observe that `vec.dedup_by(same_bucket)` calls `same_bucket(a, b)` where `b` appears before `a` in the vector, and discards `a` when true is returned. This argument order is probably a bug, but since it has already been stabilized, I guess we should document it as a feature and move on. (`Vec::dedup` also uses `==` with this unexpected argument order, but I figure that’s not important since `==` is expected to be symmetric with no side effects.)
Mark-Simulacrum
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Jul 4, 2017
Document unintuitive argument order for Vec::dedup_by relation When trying to use `dedup_by` to merge some auxiliary information from removed elements into kept elements, I was surprised to observe that `vec.dedup_by(same_bucket)` calls `same_bucket(a, b)` where `b` appears before `a` in the vector, and discards `a` when true is returned. This argument order is probably a bug, but since it has already been stabilized, I guess we should document it as a feature and move on. (`Vec::dedup` also uses `==` with this unexpected argument order, but I figure that’s not important since `==` is expected to be symmetric with no side effects.)
bors
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When trying to use
dedup_byto merge some auxiliary information from removed elements into kept elements, I was surprised to observe thatvec.dedup_by(same_bucket)callssame_bucket(a, b)wherebappears beforeain the vector, and discardsawhen true is returned. This argument order is probably a bug, but since it has already been stabilized, I guess we should document it as a feature and move on.(
Vec::dedupalso uses==with this unexpected argument order, but I figure that’s not important since==is expected to be symmetric with no side effects.)