From: "prijutme4ty (Ilya Vorontsov)" <prijutme4ty@...>
Date: 2012-04-29T01:49:42+09:00
Subject: [ruby-core:44739] [ruby-trunk - Feature #6367] #same? for Enumerable


Issue #6367 has been updated by prijutme4ty (Ilya Vorontsov).


trans (Thomas Sawyer) wrote:
> This reminds me of #sort and #sort_by, and I think both forms would be needed here too --where the later makes it possible to use a comparison besides #==.
> 
> On the other hand it reminds me of #all? as well, which makes me wonder about #any? too.
> 
> That leads me to think:
> 
>   #all_equal?{ |a| ... }
>   #all_equal_by?{ |a,b| ... }
>   #any_equal?{ |a| ... }
>   #any_equal_by?{ |a,b| ... }

As for me it's contrintuitive to have a pair of argument. In fact we need the only argument... or maybe I didn't understand how to use this function (and how to write the method)
----------------------------------------
Feature #6367: #same? for Enumerable
https://bugs.ruby-lang.org/issues/6367#change-26303

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


I realised that I frequently test if all objects in enumerable have the same feature. For example if all words have the same length (but not defined before). So I found particulary useful method Enumerable#same_by? that test this behaviour. I think it can be simply rewritten in C and included to Enumerable core methods.
Simple ruby implementation can be written just in a pair of lines (tests included):

module Enumerable
  def same?(&block)
    return true if empty?
    if block_given?
      first_result = yield(first)
      all?{|el| first_result == yield(el)}
    else
      first_result = first
      all?{|el| first_result == el}
    end
  end
end

require 'test/unit'
class TestEnumerableSame < Test::Unit::TestCase
  def test_same
    assert_equal(true, [1,3,9,7].same?(&:even?))
    assert_equal(true, [4,8,2,2].same?(&:even?))
    assert_equal(false, [1,8,3,2].same?(&:even?))
    
    assert_equal(true, %w{cat dog rat}.same?(&:length))
    assert_equal(false, %w{cat dog rabbit}.same?(&:length))
    
    assert_equal(true, %w{cat cat cat}.same?)
    assert_equal(false, %w{cat dog rat}.same?)
    
    assert_equal(true, [].same?(&:length))
    assert_equal(true, [].same?)
  end
end



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