Issue #5663 has been updated by Alexey Muranov.


Rodrigo Rosenfeld Rosas wrote:
> Alexey, what about thread safety in this case? Would the selecting return a new object?

I do not know much about threads.  I think `#selecting` can return a new object, and `#selecting!` can add lazy selection to the object on which it is called.  Those more knowledgable please comment with something wiser.
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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: 
Target version: 


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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