Ruby 2.0 Keyword Arguments Ian Anderson 

Ruby 1.9 - Hash parameters def foo(opts = {}) bar = opts.fetch(:bar, 'default') puts bar end foo # 'default' foo(bar: 'baz') # 'baz' 

Ruby 2.0 - Keyword arguments def foo(bar: 'default') puts bar end foo # 'default' foo(bar: 'baz') # 'baz' 

What if..? def foo(bar: 'default') puts bar end foo('baz') # ArgumentError: wrong number of arguments (1 for 0) 

PRINCIPLE OF MOST SURPRISE 

Keyword arguments + (optional) options def foo(bar, baz: 'qux', **options) puts [bar, baz, options] end foo(1, option: 2) # [1, 'qux', {:option => 2}] foo(1, option: 2, baz: 'notqux') # [1, 'notqux', {:option => 2}] 

Janky required keyword arguments def foo(bar: raise(ArgumentError)) puts bar end foo # ArgumentError: ArgumentError foo(bar: 'baz') # 'baz' 

Block keyword arguments whoooaaaa define_method(:foo) do |bar: 'baz'| puts bar end foo # 'baz' foo(bar: 'qux') # 'qux' 

Concrete example - Ruby 1.9 def accepts_nested_attributes_for(*attr_names) options = { :allow_destroy => false, :update_only => false } options.update(attr_names.extract_options!) options.assert_valid_keys( :allow_destroy, :reject_if, :limit, :update_only ) end 

Concrete example - Ruby 2.0 def accepts_nested_attributes_for(*attr_names, allow_destroy: false, update_only: false reject_if: nil, limit: nil ) end 

Anatomy of a Ruby 2.0 method def foo( {required_arguments, ...} {optional_arguments, ...} {*rest || more_required_arguments...} {keyword_arguments: "defaults"...} {**rest_of_keyword_arguments} {&block_capture} ) 

Method of the year. def foo(req1, req2, maybe1 = "42", maybe2 = maybe1.upcase, *args, named1: 'foo', named2: bar(named1, req2), **options, &block) end def bar(a, b) # ... end 

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