Equalizer
A simple mixin that can be used to add instance variable based equality, equivalence and inspection methods to your objects.
Usage
require "dry/core"
class GeoLocation
include Dry::Core::Equalizer(:latitude, :longitude)
attr_reader :latitude, :longitude
def initialize(latitude, longitude)
@latitude, @longitude = latitude, longitude
end
end
point_a = GeoLocation.new(1, 2)
point_b = GeoLocation.new(1, 2)
point_c = GeoLocation.new(2, 2)
point_a.inspect # => "#<GeoLocation latitude=1 longitude=2>"
point_a == point_b # => true
point_a.hash == point_b.hash # => true
point_a.eql?(point_b) # => true
point_a.equal?(point_b) # => false
point_a == point_c # => false
point_a.hash == point_c.hash # => false
point_a.eql?(point_c) # => false
point_a.equal?(point_c) # => false
Configuration options
inspect
Use inspect option to skip #inspect method overloading:
class Foo
include Dry::Core::Equalizer(:a, inspect: false)
attr_reader :a, :b
def initialize(a, b)
@a, @b = a, b
end
end
Foo.new(1, 2).inspect
# => "#<Foo:0x00007fbc9c0487f0 @a=1, @b=2>"
immutable
For objects that are immutable it doesn't make sense to calculate #hash every time it's called. To memoize hash use immutable option:
class ImmutableHash
include Dry::Core::Equalizer(:foo, :bar, immutable: true)
attr_accessor :foo, :bar
def initialize(foo, bar)
@foo, @bar = foo, bar
end
end
obj = ImmutableHash.new('foo', 'bar')
old_hash = obj.hash
obj.foo = 'changed'
old_hash == obj.hash
# => true