Named parameters in Ruby 2

The last example you posted is misleading. I disagree that the behavior is similar to the one before. The last example passes the argument hash in as the first optional parameter, which is a different thing!

If you do not want to have a default value, you can use nil.

If you want to read a good writeup, see "Ruby 2 Keyword Arguments".

I think that the answer to your updated question can be explained with explicit examples. In the example below you have optional parameters in an explicit order:

def show_name_and_address(name="Someone", address="Somewhere")
  puts "#{name}, #{address}"
end

show_name_and_address
#=> 'Someone, Somewhere'

show_name_and_address('Andy')
#=> 'Andy, Somewhere'

The named parameter approach is different. It still allows you to provide defaults but it allows the caller to determine which, if any, of the parameters to provide:

def show_name_and_address(name: "Someone", address: "Somewhere")
  puts "#{name}, #{address}"
end

show_name_and_address
#=> 'Someone, Somewhere'

show_name_and_address(name: 'Andy')
#=> 'Andy, Somewhere'

show_name_and_address(address: 'USA')
#=> 'Someone, USA'

While it's true that the two approaches are similar when provided with no parameters, they differ when the user provides parameters to the method. With named parameters the caller can specify which parameter is being provided. Specifically, the last example (providing only the address) is not quite achievable in the first example; you can get similar results ONLY by supplying BOTH parameters to the method. This makes the named parameters approach much more flexible.

As of Ruby 2.1.0, you no longer have to set default values for named parameters. If you omit the default value for a parameter, the caller will be required to provide it.

def concatenate(val1: 'default', val2:)
  "#{val1} #{val2}"
end

concatenate(val2: 'argument')
#=> "default argument"

concatenate(val1: 'change')
#=> ArgumentError: missing keyword: val2

---

Given:

def test1(var1="default value123")
  var1
end

def test2(var1:"default value123")
  var1
end

They'll behave the same way when not passed an argument:

test1
#=> "default value123"

test2
#=> "default value123"

But they'll behave much differently when an argument is passed:

test1("something else")
#=> "something else"

test2("something else")
#=> ArgumentError: wrong number of arguments (1 for 0)


test1(var1: "something else")
#=> {:var1=>"something else"}

test2(var1: "something else")
#=> "something else"

I agree with you that it's weird to require default values as the price for using named parameters, and evidently the Ruby maintainers agree with us! Ruby 2.1 will drop the default value requirement as of 2.1.0-preview1.