arguments-1.rb

def foo(options = {})
  [options[:bar], options[:baz]]
end

foo(bar: '12345', baz: 'abcdef') # => ["12345", "abcdefg"]

arguments-2.rb

def foo(options = {})
  options = { bar: '12345', baz: 'abcdef' }.merge!(options)
  [options[:bar], options[:baz]]
end

foo                         # => ["12345", "abcdefg"]
foo(bar: 'bar')             # => ["bar", "abcdef"]
foo(bar: 'bar', baz: 'baz') # => ["bar", "baz"]

arguments-3.rb

def foo(bar: '12345', baz: 'abcdef')
  [bar, baz]
end

foo                         # => ["12345", "abcdefg"]
foo(bar: 'bar')             # => ["bar", "abcdef"]
foo(bar: 'bar', baz: 'baz') # => ["bar", "baz"]

arguments-4.rb

def foo(value, bar: '12345', baz: 'abcdef')
  [value, bar, baz]
end

foo('VALUE')                         # => ["VALUE", "12345", "abcdefg"]
foo('VALUE', bar: 'bar')             # => ["VALUE", "bar", "abcdef"]
foo('VALUE', bar: 'bar', baz: 'baz') # => ["VALUE", "bar", "baz"]

array-literals.rb

allowed_methods = %i(get post put)

allowed_methods # => [:get, :post, :put]

to_h.rb

Car = Struct.new(:brand, :model, :color)

sporty = Car.new('Chevrolet', 'Corvette', 'Red')

sporty.to_h  # => {:brand=>"Chevrolet", :model=>"Corvette", :color=>"Red"}