[ruby-core:61292] [ruby-trunk - Feature #5663] Combined map/select method

Issue #5663 has been updated by Tsuyoshi Sawada.


Also, regarding Yehuda Katz's concern:

> The only caveat is that it would be impossible to intentionally return nil here; suggestions welcome.

I would like to propose that the method takes an optional argument that determines what element is to be removed. By default, this is `nil`.

    [1, 2, 3, 4].partial_map{|i| i + 4 if i.even?} # => [6, 8]

    s = "abc"
    [0, 1, 2, 3, 4].partial_map(:ignore){|i| i.even? s[i] : :ignore} # => ["a", "c", nil]


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Feature #5663: Combined map/select method
https://bugs.ruby-lang.org/issues/5663#change-45623

* Author: Yehuda Katz
* Status: Assigned
* Priority: Normal
* Assignee: Yukihiro Matsumoto
* Category: lib
* Target version: next minor
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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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