Issue #5663 has been updated by alexeymuranov (Alexey Muranov).


=begin
By the way, is anybody using the (({nil})) returned by (({#compact!})) ?

  enum.map { |i| i + 1 if i.even? }.compact

makes un unnecessary copy, but i cannot use

  enum.map { |i| i + 1 if i.even? }.compact!

because it will return (({nil})) if no changes were made.

Wouldn't it be better if (({#compact})) and (({#compact!})) returned the same thing?
=end

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Feature #5663: Combined map/select method
https://bugs.ruby-lang.org/issues/5663#change-26908

Author: wycats (Yehuda Katz)
Status: Feedback
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: lib
Target version: 2.0.0


It is pretty common to want to map over an Enumerable, but only include the elements that match a particular filter. A common idiom is:

enum.map { |i| i + 1 if i.even? }.compact

It is of course also possible to do this with two calls:

enum.select { |i| i.even? }.map { |i| i + 1 }

Both cases are clumsy and require two iterations through the loop. I'd like to propose a combined method:

enum.map_select { |i| i + 1 if i.even? }

The only caveat is that it would be impossible to intentionally return nil here; suggestions welcome. The naming is also a strawman; feel free to propose something better.


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