Issue #5663 has been updated by Rodrigo Rosenfeld Rosas.


Thomas, I didn't find your example for justifying a "null" instance good enough. Why not just using "nil" instead of "foo"?

But I liked your suggestion on "compact" allowing an argument defaulting to nil.

Joshua, I like the idea of next inside a map doing the compact thing, but I guess this will be hard to get approval for from Ruby Core team.

It would be a surprising feature in Ruby. Ruby is usually a pretty concise language with very little surprises... I'm not sure if they'll want to introduce such different "next" behavior only for the map/collect method.
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Feature #5663: Combined map/select method
https://bugs.ruby-lang.org/issues/5663

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