===.rb

RUBY_VERSION                    # => "2.7.0"

def foo?(str)
  case str
  when "foo" then true
  else false
  end

  # "foo" === str
end

foo?("foo")                     # => true
foo?("bar")                     # => false
foo?(0)                         # => false
foo?(nil)                       # => false

"foo" === "foo"                 # => true
"foo" === "bar"                 # => false

  
def string?(x)
  case x
  when String then true
  else false
  end
end

string?("foo")                  # => true
string?(1)                      # => false

"foo".is_a? String              # => true
String === "foo"                # => true
"foo" === String                # => false


def enumerable?(x)
  case x
  when Enumerable then true
  else false
  end
end

enumerable?("foo")              # => false
enumerable?(2)                  # => false
enumerable?([2])                # => true
enumerable?(2..3)               # => true
enumerable?({})                 # => true
enumerable?(nil)                # => false