What is the effect of hash and eq implementation in Ruby

Question

class A
  def hash
    12
  end

  def ==(other)
    true
  end
end

x = {}
a = A.new
b = A.new
x[a] = "Hello"
x[b] = "World"
puts x

This is printing:
{#<A:0x000055d1f3985c68>=>"Hello", #<A:0x000055d1f3985830>=>"World"}

I expected replacement, not happening, why?

Answer 1

Two objects are treated as the same hash key when their hash value is identical and the two objects are eql? to each other.

http://www.ruby-doc.com/3.3.0/Hash.html#class-Hash-label-Hash+Key+Equivalence

You have to define eql? instead of ==:

class A
  def hash
    1
  end

  def eql? other
    true
  end
end

x = {}
a = A.new 
b = A.new

x[a] = "Hello"
x[b] = "World"

p x

#=> {#<A:0x00007fce035af608>=>"World"}