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https://twitter.com/m_ou_se/status/1542556414752718848
前々から思っていたけど、「コンテナ内における整理用に使う equality / ordering」と「自然な解釈を伴うデータとしての equality / ordering」って別概念だよね。本来は。
TwitterMara Bos on Twitter“The floating point types, f32 and f64, now have a method called `total_cmp` to compare them using a total ordering that includes NaN, instead of the usual partial ordering in which NaN is unordered.
This is especially useful when sorting floats.
See https://t.co/CBefEI02SR
6/9”
たとえば enum を定義してやるとして「variant 同士に自然な解釈にもとづく ordering は存在しない」と「その enum を key として BTreeMap に入れたり、その enum の Vec を整列することで正規化するようなことを許したい」みたいなのって、完全に両立するわけで
Two distinct use of ordering: semantic ordering and... systematic ordering? - language design - Rust Internals
https://internals.rust-lang.org/t/two-distinct-use-of-ordering-semantic-ordering-and-systematic-ordering/16921
あんまり気になったものだから IRLO に投げてみた
Rust InternalsTwo distinct use of ordering: semantic ordering and... systematic ordering?I feel there are two kinds of "ordering". One is "semantic" ordering, which arises when users (especially the humanity) interpret the value. And the other is... let's call it "systematic" ordering, which is required to put into or retrieve from containers, but not necessarily brings natural interpretation. I think that the meaning and use of Cmp is ambiguous. Does (or should) developers implement it as "semantic" ordering, or "systematic" ordering? And, does users always consider it as "semanti...