[tyingq]

Does the pattern matching do something that Ruby's map() can't do?

Coming from Perl, map() there can return fewer elements than the source list, so pattern matching works already. A short skim of Ruby's map seems to imply it always returns something with the same number of elements.

Edit: I was confused about what this feature did. So this subthread is still interesting, but mostly unrelated.

[rubyfan]

Yeah afaik something is always returned from the block (even if it’s nil). Occasionally I recall my self doing something where the block might return nil and then I’d call `compact` to get rid of extra nil stuff. It works when you want a modified version of the enumerable but don’t want nil stuff. If you just want to match a subset then I think `select` is probably what you want.

Further, the pattern matching feature is significantly different than `map` imo.

[knrz]

In JavaScript, Elixir, and Ruby I use flatMap for this purpose. You can return an empty array on the block to “skip” over the element.

[Rafert]

2.7 introduces `Enumerable#filter_map` for that. Example from the NEWS file:

[1, 2, 3].filter_map {|x| x.odd? ? x.to_s : nil } #=> ["1", "3"]

[s_kilk]

Map is data manipulation, whereas pattern-matching is control flow.

[tyingq]

Yes, thank you. Reading the sub linked presentation, I see it now.

The sentence "It can traverse a given object and assign its value if it matches a pattern" sounded like traverse and (optionally) manipulate.