Issue #6483 has been updated by matz (Yukihiro Matsumoto).

Status changed from Assigned to Rejected

I reject the original idea of #pmap which might be read as 'parallel map' or 'parametric map' or something else.
The idea of adding parameter to block with argument specified e.g. a.map(&:to_s.(2)) is interesting,
but it must be proposed in separated issue.

Matz.

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Feature #6483: parametric map
https://bugs.ruby-lang.org/issues/6483#change-33321

Author: prijutme4ty (Ilya Vorontsov)
Status: Rejected
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: 
Target version: next minor


I found very common use-case for map: map with parameters and &:meth syntax. For example:
matrix =[[1,2,3],[4,5,6]]
matrix.pmap(' ',&:join).join("\n") # => "1 2 3\n4 5 6
[1,2,3,4,5].pmap(2, &:to_s) # ['1', '10', '11', '100', '101']

[1,2,3,4,5].pmap(&:to_s) # ['1', '2, '3', '4', '5'] # empty parameter list behaves as usual map

Isn't it much better than ugly and verbose code: 
matrix.map{|line| line.join(' ')}.join("\n")

I can write simple implementation 
class Proc
  def curry_except_self(*args)
    Proc.new{|slf| curry[slf,*args] }
  end
end

module Enumerable
  def pmap!(*args,&block)
    map! &block.curry_except_self(*args)
  end
  def pmap(*args,&block)
    dup.pmap!(*args, &block)
  end
end

Use-cases can be rewritten as tests (I can send my own unit-test if needed)


Also I've two related things to discuss.
1) First is &-syntax. Is it possible to change ruby-interpeter in such a way that &:proc could be at any place. matrix.pmap(&:join,' ') is much prettier than matrix.join(' ',&:join) What is the reason behind this restriction? And if one can remove this restriction, we'd have new nice syntax.
2) I'm not very experience in functional programming with curry etc, but it seems to me that currying proc without supplying first argument(self) can be common task when &:meth syntax is in play. If so, may be my curry_except_self(*args) also should be included in ruby.


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