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?
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Does this answer your question? Is there a Ruby method for determining if all instance variables of two instances of the same class are equal?ggorlen– ggorlen2021-08-22 02:22:27 +00:00Commented Aug 22, 2021 at 2:22
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4 Answers
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
3 Comments
dfens
But what if i want to do this using other classes? Or if there are 100 attributes?
Jason Noble
In your ==(other) method, you could do self.instance_variables.each do |ivar| self.ivar == other.ivar end You may want to look at === as well.
yurisich
Using
Struct or OpenStruct has these sorts of cases built into them.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
2 Comments
dfens
This seems fine but I need this functionality for objects, anyway nice response I didn't know about Structs
sepp2k
@dfens: Those are objects.
Struct.new is just a factory method for classes. You'd get the exact same behavior if you'd define Aaa using the class keyword and then defined == etc. yourself.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
Comments
Extra method to deal with comparing objects in Ruby consists in using hash. For performance reason, when the class are huge, the best is to use hash to compare ruby objects as so :
class Aaa
attr_accessor :a, :b
def intialize(value_a,value_b)
@a = value_a
@b = value_b
end
def hash(target)
@a.hash == target.a.hash && @b.hash == target.b.hash
end
end
A = new Aaa('whatever','whenever')
B = new Aaa('however','whoever')
A.hash(B)
1 Comment
Diego
This won't work as expected. Two different unequal objects can have the same hash value and the same object may not have the same hash value between invocations of Ruby. Furthermore, #hash is supposed to return an integer, not a boolean. This is only useful to do a quick check to see if two values might be equal, and for bucketing keys in a Hash for quick lookup. ruby-doc.org/3.2.1/Object.html#method-i-hash