Comparing objects in ruby

Question

Consider this:

class Aaa
  attr_accessor :a, :b
end

x = Aaa.new
x.a, x.b = 1,2
y = Aaa.new
y.a, y.b = 1,2

puts x == y #=>false

Is there some way to check if all public attributes are equal in classes of same type?

Answer 1

class Aaa
  attr_accessor :a, :b

  def ==(other)
    return self.a == other.a && self.b == other.b
  end
end

x = Aaa.new
x.a,x.b = 1,2
y = Aaa.new
y.a,y.b = 1,2
y = Aaa.new
y.a,y.b = 1,2
z = Aaa.new
z.a,z.b = 1,3

x == y # => true
x == z # => false

Answer 2

Aaa = Struct.new(:a, :b)

x = Aaa.new
x.a, x.b = 1,2
y = Aaa.new
y.a, y.b = 1,2

x == y #=> true

Struct defines ==, eql?, and hash for you, so that two Aaas are equal, if their values for a and b are equal. It also defines initialize so that you can optionally pass in the values for a and b when creating the object (Aaa.new(value_for_a, value_for_b)). And it defines to_a to return [a,b].

You can also use Struct.new with a block to define additional methods, so you have the full power of a "normal" class:

Aaa = Struct.new(:a, :b) do
  def c
    a+b
  end
end
Aaa.new(23,42).c #=> 65

Answer 3

We can easily generalize to any number of instances and drop the requirement for getters for the instance variables:

class Aaa
  def initialize(a,b,c)
    @a, @b, @c = a, b, c
  end
end

x = Aaa.new(1,2,3)
y = Aaa.new(1,2,3)
z = Aaa.new(1,2,3)
arr = [x,y,z]

x.instance_variables.map do |v|
  arr.map { |i| i.send(:instance_variable_get,v) }.uniq.size == 1
end.all?
  #=>true

Change z to:

z = Aaa.new(1,2,4)

then:

x.instance_variables.map do |v|
  arr.map { |i| i.send(:instance_variable_get,v) }.uniq.size == 1
end.all?
  #=> false