How do methods use hash arguments in Ruby?

Question

I saw hash arguments used in some library methods as I\'ve been learning.

E.g.,

list.search(:titles, genre: \'jazz\', duration_less_than: 270)
         


        

Answer 1

When a Ruby method call's argument list ends in one or more key-value pairs, like foo: 'bar' or 'foo' => 1, Ruby collects them all into a single hash and passes that hash as the last parameter. You can see that yourself in irb:

irb(main):002:0> puts foo: 'bar', baz: 'quux'
{:foo=>"bar", :baz=>"quux"}
=> nil

Thus, you can add a final, optional parameter to a method you're writing to receive this hash. You'll usually want to default it to an empty hash. You can call the parameter anything you want, but options is a common name:

def my_method(a, b, c, options = {})
  ...
end

One useful trick if you're using Rails: It's often handy to treat plain strings and symbols as equivalent. Rails adds a symbolize_keys! method to Hash to convert all string keys to symbols:

def my_method(a, b, c, options = {})
  options.symbolize_keys!
  ...
end