Feature #5044: #zip with block return mapped results

• Status: Rejected
• Priority: Normal
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[trans (Thomas Sawyer)]

Is there any reason that #zip doesn't return results like map?

[1,2,3].zip([1,2,3]){ |a,b| a + b } #=> [2,4,6]

Currently, it just returns nil, which seems rather contrary to the return result of the non-block form.

[Eregon (Benoit Daloze)]

Hi,

Please have a look at http://redmine.ruby-lang.org/issues/4539 (or [ruby-core:35613]).

The reason is explained by Yusuke in [ruby-core:35682]:

2011/4/5 Benoit Daloze [e-mail]:

An unconditional nil is anyway not useful here, the only concern I see
might be the cost of creating this Array.

It is actually a problem.
I have used Array#zip with block for iteration many times.

big_ary1.zip(big_ary2) do |x, y|
p [x, y]
end

The change requires some people (including me) to rewrite
such a code as follows:

big_ary1.size.times do |i|
x, y = big_ary1[i], big_ary2[i]
...
end

So I like zip_with, if it is really needed.

That issue kind of got lost, it is probably a good idea to continue it.

For your example, we could have [1,2,3].zip_with([1,2,3], :+)

[akr (Akira Tanaka)]

Currently it can be implemented as follows.

% ruby -e 'p [1,2,3].zip([1,2,3]).map {|a,b| a + b }'
[2, 4, 6]
% ruby -e 'p [1,2,3].lazy.zip([1,2,3]).map {|a,b| a + b }.to_a'
[2, 4, 6]

[mame (Yusuke Endoh)]

• Status changed from Open to Assigned
• Assignee set to matz (Yukihiro Matsumoto)

[mame (Yusuke Endoh)]

• Target version set to 2.6

[naruse (Yui NARUSE)]

• Target version deleted (2.6)

[matz (Yukihiro Matsumoto)]

• Status changed from Assigned to Rejected

We cannot change the behavior. The change would increase the memory consumption (and decrease the performance).

Matz.

[duerst (Martin Dürst)]

• Related to Feature #16261: Enumerable#each_splat and Enumerator#splat added