Understanding equality in your Ruby codez https://github.com/gsterndale/equality

1. All Objects Are Created .equal?
Understand equality in your Ruby codez

2. github.com/gsterndale/equality

3. Equality methods
a == b
a === b
a.eql? b
a.equal? b

4. ==

5. Everyday equality (==)
a == b

6. Default ==
a = MyBasicClass.new
b = MyBasicClass.new
a == b
# => false
b = a
a == b
# => true

7. Overriding ==
class RomanNumeral
def ==(other)
if other.respond_to?(:to_f)
self.to_f == other.to_f
else
false
end
end
end

8. Overriding ==
iv = RomanNumeral.new('IV')
iiii = RomanNumeral.new('IIII')
iv == iiii
# => true

9. ===

10. case statement equality (===)
a === b

11. Default ===
a = Object.new
b = Object.new
case a
when b
'b must === a'
else
'b must NOT === a'
end
# => "b must NOT === a"

12. Float ===
a = 1
b = 1.0
case a
when b
'b must === a'
else
'b must NOT === a'
end
# => "b must === a"

13. Regexp ===
case '123'
when /d+/
'At least one number'
else
'No numbers found'
end
# => "At least one number"

14. When === != ==
/d+/ == '123'
# => false
/d+/ === '123'
# => true

15. Class ===
case 'abc'
when String
'It is a String!'
else
'Not a String'
end
# => "It is a String!"

16. Asymmetry
/d+/ === '123'
# => true
'123' === /d+/
# => false

17. Asymmetry
2 === Integer
# => false
Integer === 2
# => true
Fixnum === 2
# => true

18. .equal?

19. Object equality (.equal?)
a = 'FOO'
b = a
a.equal? b
# => true
a.equal? 'FOO'
# => false

20. .eql?

21. Hash key equality (.eql?)
a.eql? b

22. Default .eql?
foo = Object.new
hash = { foo => 'My value' }
bar = Object.new
foo.equal? bar
# => false
foo.eql? bar
# => false
hash[bar]
# => nil

23. String .eql?
foo = 'My Key'
hash = { foo => 'My value' }
bar = 'My Key'
foo.equal? bar
# => false
foo.eql? bar
# => true
hash[bar]
# => "My value"

24. Overriding .eql?
class RomanNumeral
def eql?(other)
other.kind_of?(RomanNumeral) &&
self.to_i.eql?(other.to_i)
end
end

25. Overriding .eql?
iv = RomanNumeral.new('IV')
hash = { iv => 'Four' }
iiii = RomanNumeral.new('IIII')
iv.equal? iiii
# => false
iv.eql? iiii
# => true
hash[iiii]
# => "Four"

26. Comparable

27. Comparison methods
# You must define <=>
a <=> b
# => -1, 0, 1 -or- nil
a == b
a > b
a < b
a >= b
a <= b
c.between?(a, b)

28. Overriding <=>
class RomanNumeral
def <=>(other)
if other.respond_to?(:to_f)
self.to_f <=> other.to_f
else
nil
end
end
end

29. Overriding <=>
v = RomanNumeral.new('V')
x = RomanNumeral.new('X')
v <=> x
# => -1
v >= x
# => false
RomanNumeral.new('VIII').between?(v, x)
# => true

30. Sorting Enumerables
iv = RomanNumeral.new('IV')
iiii = RomanNumeral.new('IIII')
x = RomanNumeral.new('X')
[iv, x, iiii]
# => [IV, X, IIII]
[iv, x, iiii].sort
# => [IV, IIII, X]