Can I have required named parameters in Ruby 2.x?

Ruby 2.0 is adding named parameters, like this:

def say(greeting: 'hi')
  puts greeting
end

say                     # => puts 'hi'
say(greeting: 'howdy')  # => puts 'howdy'

How can I use named parameters without giving a default value, so that they are required?

There is no specific way in Ruby 2.0.0, but you can do it Ruby 2.1.0, with syntax like def foo(a:, b:) ...

In Ruby 2.0.x, you can enforce it by placing any expression raising an exception, e.g.:

def say(greeting: raise "greeting is required")
  # ...
end

If you plan on doing this a lot (and can't use Ruby 2.1+), you could use a helper method like:

def required
  method = caller_locations(1,1)[0].label
  raise ArgumentError,
    "A required keyword argument was not specified when calling '#{method}'"
end

def say(greeting: required)
  # ...
end

say # => A required keyword argument was not specified when calling 'say'