From: Rodrigo Rosenfeld Rosas <rr.rosas@...>
Date: 2012-02-13T20:43:39+09:00
Subject: [ruby-core:42531] [ruby-trunk - Feature #5663] Combined map/select method


Issue #5663 has been updated by Rodrigo Rosenfeld Rosas.


I don't think #4890 removes the need for this ticket. This is about API, not implementation. Even if we can use lazy maps/collects to implement this API, I still think it should exist.
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Feature #5663: Combined map/select method
https://bugs.ruby-lang.org/issues/5663

Author: Yehuda Katz
Status: Rejected
Priority: Normal
Assignee: 
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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