Determining class of an object with case equality operator (===)


Case equality operator (or triple equals, ===) in Ruby returns true if the passed class is in the ancestors list of the passed object's class:


1.class.ancestors # [Integer, Numeric, Object, ...]

Numeric === 1 # true

Object === 1 # true

So it can be used for determining object's class:


String === 'abc' # true

'abc'.class #=> String

In cases above the case equality operator works like #kind_of? (or #is_a?):


1.kind_of?(Integer) # true

1.is_a?(Numeric) # true

The classes above has different implementations of === operator, that's why the results of comparison are different:


String.===('abc') # the same as String === 'abc'

Also it means that order of the arguments is important:


1 === Integer # false


Alexander
Spitsyn

Full-Stack Developer at JetRockets

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