Ruby Language Methods Capturing undeclared keyword arguments (double splat)
Example
The ** operator works similarly to the * operator but it applies to keyword parameters.
def options(required_key:, optional_key: nil, **other_options)
other_options
end
options(required_key: 'Done!', foo: 'Foo!', bar: 'Bar!')
#> { :foo => "Foo!", :bar => "Bar!" }
In the above example, if the **other_options is not used, an ArgumentError: unknown keyword: foo, bar error would be raised.
def without_double_splat(required_key:, optional_key: nil)
# do nothing
end
without_double_splat(required_key: 'Done!', foo: 'Foo!', bar: 'Bar!')
#> ArgumentError: unknown keywords: foo, bar
This is handy when you have a hash of options that you want to pass to a method and you do not want to filter the keys.
def options(required_key:, optional_key: nil, **other_options)
other_options
end
my_hash = { required_key: true, foo: 'Foo!', bar: 'Bar!' }
options(my_hash)
#> { :foo => "Foo!", :bar => "Bar!" }
It is also possible to unpack a hash using the ** operator. This allows you to supply keyword directly to a method in addition to values from other hashes:
my_hash = { foo: 'Foo!', bar: 'Bar!' }
options(required_key: true, **my_hash)
#> { :foo => "Foo!", :bar => "Bar!" }
