Expose ComposedFunction as a public API #37517
Update base/operators.jl
Co-authored-by: Jonas Schulze <[email protected]>
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I would actually prefer to name the fields to e.g.
outer, innerinstead off,g. It is hard to remember if this modelsf∘gorg∘f.There was a problem hiding this comment.
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I'm somewhat neutral about the choice of the field names. I see
fandgas something likexandy. It's technically arbitrary but I've seen it many times so I don't think it's super hard to guess the ordering.Just as a note, one (rather weak) upside of keep using
fandgis that we can defineComposedFunctionfor olderjuliaversions as done in DataFrames.jl (JuliaData/DataFrames.jl#2274 (comment)). However, it doesn't matter much since 1.6 soon will be the LTS (and we can even definegetpropertyfor the closure in Compat.jl).There was a problem hiding this comment.
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I think the order is not easy to guess at all. Just have a look at the wikipedia article. There the order
g∘fis more dominant, which is opposed to the current order we use.There was a problem hiding this comment.
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My personal first guess was btw
g∘f.There was a problem hiding this comment.
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Well, I sometimes get inner/outer opposite somehow (though this is probably just me). Since you can always flip the arrows (and which direction feels natural depends on the context), I'm not sure if there are truly unambiguous names for them. But I'm likely nitpicking. I agree inner/outer is more descriptive for function composition.
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With
outer, innerit is at least clear thatc::ComposedFunctiontalks aboutc.outer(c.inner(x)). Withf,git is unclear whether we are talking aboutc.f(c.g(x))orc.g(c.f(x)). Remembering the direction of arrows is an independent problem that comes up in both scenarios.There was a problem hiding this comment.
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Btw, I also get inner outer wrong sometimes, but I can usually recover by pure reasoning without having to dig up the source.
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I agree it's easier to remember and be confident which function is applied first with inner/outer. I think I'm in the team inner/outer now. How about renaming them in this PR and see the reactions of other reviewers?
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For the little it is worth, I think
fandgare fine and their exact interpretation can be clarified in the docstring. That way there doesn't need to be any work on Compat.jl or in other packages.If you stick with inner and outer, then I think line 881 needs to change:
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No,
fandgare confusing, we should not force people to look up the docstring all the time. Also @tkf has a PR to compatJuliaLang/Compat.jl#720 and supporting
fandgis the easy part of that code.