class Concurrent::Map

def put_if_absent(key, value)

Returns:

(Object, nil) - the previous value when key was present or nil when there was no key

Parameters:

value (Object) --
key (Object) --

def put_if_absent(key, value)
  computed = false
  result   = compute_if_absent(key) do
    computed = true
    value
  end
  computed ? nil : result
end unless method_defined?(:put_if_absent)