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Uploaded bygsterndale
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All Objects are created .equal?

The document discusses different equality methods in Ruby - ==, ===, .equal?, .eql?, and <=> (comparable). It explains how each works by default, and how their behavior can be overridden for custom classes. Overriding methods like ==, .eql?, and <=> allows custom classes to be compared and sorted as needed.

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All Objects Are Created .equal? Understand equality in your Ruby codez
github.com/gsterndale/equality
Equality methods a == b a === b a.eql? b a.equal? b
==
Everyday equality (==) a == b
Default == a = MyBasicClass.new b = MyBasicClass.new a == b # => false b = a a == b # => true
Overriding == class RomanNumeral def ==(other) if other.respond_to?(:to_f) self.to_f == other.to_f else false end end end
Overriding == iv = RomanNumeral.new('IV') iiii = RomanNumeral.new('IIII') iv == iiii # => true
===
case statement equality (===) a === b
Default === a = Object.new b = Object.new case a when b 'b must === a' else 'b must NOT === a' end # => "b must NOT === a"
Float === a = 1 b = 1.0 case a when b 'b must === a' else 'b must NOT === a' end # => "b must === a"
Regexp === case '123' when /d+/ 'At least one number' else 'No numbers found' end # => "At least one number"
When === != == /d+/ == '123' # => false /d+/ === '123' # => true
Class === case 'abc' when String 'It is a String!' else 'Not a String' end # => "It is a String!"
Asymmetry /d+/ === '123' # => true '123' === /d+/ # => false
Asymmetry 2 === Integer # => false Integer === 2 # => true Fixnum === 2 # => true
.equal?
Object equality (.equal?) a = 'FOO' b = a a.equal? b # => true a.equal? 'FOO' # => false
.eql?
Hash key equality (.eql?) a.eql? b
Default .eql? foo = Object.new hash = { foo => 'My value' } bar = Object.new foo.equal? bar # => false foo.eql? bar # => false hash[bar] # => nil
String .eql? foo = 'My Key' hash = { foo => 'My value' } bar = 'My Key' foo.equal? bar # => false foo.eql? bar # => true hash[bar] # => "My value"
Overriding .eql? class RomanNumeral def eql?(other) other.kind_of?(RomanNumeral) && self.to_i.eql?(other.to_i) end end
Overriding .eql? iv = RomanNumeral.new('IV') hash = { iv => 'Four' } iiii = RomanNumeral.new('IIII') iv.equal? iiii # => false iv.eql? iiii # => true hash[iiii] # => "Four"
Comparable
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)
Overriding <=> class RomanNumeral def <=>(other) if other.respond_to?(:to_f) self.to_f <=> other.to_f else nil end end end
Overriding <=> v = RomanNumeral.new('V') x = RomanNumeral.new('X') v <=> x # => -1 v >= x # => false RomanNumeral.new('VIII').between?(v, x) # => true
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]