From: Nobuyoshi Nakada <nobu@...>
Date: 2011-11-25T12:00:56+09:00
Subject: [ruby-core:41294] [ruby-trunk - Feature #5663] Combined map/select method


Issue #5663 has been updated by Nobuyoshi Nakada.


Rodrigo Rosenfeld Rosas wrote:
> Nobuyoshi, wouldn't &:even? be equivalent to :even?.to_proc? I just find that the example reads better this way ;)

They are different.
&expr calls #to_proc method on the result of expr, to achieve a Proc object.

> (1..10).grep(&:even?){|i|i+1}

It's a syntax error.

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Feature #5663: Combined map/select method
http://redmine.ruby-lang.org/issues/5663

Author: Yehuda Katz
Status: Open
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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