Issue #10426 has been reported by Tsuyoshi Sawada.

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Feature #10426: A predicate to express congruence
https://bugs.ruby-lang.org/issues/10426

* Author: Tsuyoshi Sawada
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
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I occasionally felt the necessity of a predicate that checks congruence with respect to some operations:

~~~ruby
class Object
	def equal_by? other, &pr
		pr.call(self) == pr.call(other)
	end
	alias congruent? equal_by?
end

5.congruent?(2){|e| e % 3} #=> true
"HELLO".equal_by?("Hello", &:downcase) #=> true
~~~



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