**args as function parameter in Ruby

Question

I understand that **args is interpreted as a hash containing all key value pairs passed to a function but I don't understand why that would be preferred over a typical parameter. For example, I have the following two functions.

def test(some_string, hash)
    puts hash
    puts hash.class # => Hash
end


def test_two(some_string, **hash)
    puts hash
    puts hash.class # => Hash
end 

calling test("test string", a: 1, b: 2) or test_two("test string", a: 1, b: 2) produces the exact same result. What is the benefit of using ** as a parameter value?

Answer 1

Ruby 2.7 started more clearly differentiating between keyword arguments and regular hashes. **args is for keyword arguments. Some implications:

def test3(some_string, foo:, **args)
  puts args
end

test3('a', foo: 'b', bar: 'c') # => {:bar=>"c"}

works as expected, however

def test3(some_string, foo:, hash)
  puts args
end # => syntax error

def test3(some_string, hash, foo:)
  puts args
end # works so far

test3('a', foo: 'b', bar: 'c')
# warning: Passing the keyword argument as the last hash parameter is deprecated
# ArgumentError (missing keyword: :foo)

Once you upgrade to ruby 3, the warnings turn to errors.