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"Useless syntax sugar": Numbered block parameters in Ruby
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this post was submitted on 11 Oct 2023
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Programming
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It wouldn't be as relevant, since passing a function or method instead of a closure is much easier in Rust - you can just name it, while Ruby requires you to use the
methodmethod.So instead of
.map(|res| res.unwrap())you can do.map(Result::unwrap)and it'll Just Work™.Except when Type::Method takes a reference, then it doesn't just work
Well, that's to be expected - the implementation of
mapexpects a function that takes ownership of its inputs, so you get a type mismatch.If you really want to golf things, you can tack your own
map_ref(and friends) onto theIteratortrait. It's not very useful - the output can't reference the input - but it's possible!I imagine you could possibly extend this to a combinator that returns a tuple of
(Input, ref_map'd output)to get around that limitation, although I can't think of any cases where that would actually be useful.In the case of your example we'd do
.map(&:unwrap)in Ruby (if unwrap was a method we'd actually want to call)Notably, these are not the cases
_1and_2etc are for. They are there for the cases that are not structurally "call this method on the single argument to the block" e.g..map{ _1 + _2 }or.map { x.foo(_1) }(
_1is reasonable, because iterating over an enumerable sequence makes it obvious what it is;_1and_2combined is often reasonable, because e.g. if we iterate over a key, value enumerable, such as what you get from enumerating aHash, it's obvious what you get; if you find yourself using_3or above, you're turning to the dark side and should rethink your entire life)