Add Triple Equals: The Case Equality Operator as a Ruby til

ruby/triple-equals-the-case-equality-operator.md

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+# Triple Equals: The Case Equality Operator
+
+The standard equality operator in Ruby is the double equals (`==`).
+
+```ruby
+> 2 + 2 == 4
+=> true
+```
+
+Ruby supports another operator that looks sneakily like this, but with
+different behavior. It's the triple equals (`===`) which is called the [case
+equality
+operator](https://ruby-doc.org/core-3.0.3/Object.html#method-i-3D-3D-3D) (or
+case subsumption operator).
+
+Though the specific behavior can be overridden on a class by class basis, the
+operator is generally used to check if the first operand is a bucket that the
+second operand fits into.
+
+Here are some examples:
+
+```ruby
+> (1..10) === 5
+=> true
+> (1..10) === 13
+=> false
+
+> Integer === 7
+=> true
+> Integer === 'nope'
+=> false
+
+> /fun/ === "fundamentals"
+=> true
+> /taco/ === "fundamentals"
+=> false
+
+> Object === String
+=> true
+> String === Object
+=> false
+```
+
+It's important to understand how this works because `===` is the operator used
+under the hood by Ruby's case statements.
+
+[source](https://stackoverflow.com/questions/4467538/what-does-the-operator-do-in-ruby/4467823#4467823)