While working on documenting things I learned through a Learn Ruby By Testing project, I came across documenting the new Ruby 2.0 ‘Params’ feature.

I realized that Methods are blocks and Procs and lambdas are very close, so was wondering if the arguments would cross over.

It turns out that it does. If you are not familiar with the new “named parameters” feature, it works by taking a Hash argument, along with another new syntax that starts with a two asterisks. Similar to the “optional argument” syntax, it basically accepts all other non-named hash keys that you would give your method. Or, Proc or lambda.

Let’s look at the signature:

def some_method(*args, name: 'Joe', age: 23, **additional_params)

This describes an argument list consisting of an 0 or more arguments for *args, a named parameter called name, with the value of ‘Joe’ by default, and a named parameter of age, with a default value of 23, and at the end, the syntax that allows you to pass in arbitrary number of hash keys, with values.

It is important to note that in order to have the **additional_params at the end, after the normal Hash that you may be used it, you must use the Ruby 1.9 syntax of key: value, rather than :key => valueor it will break.

Well, that is wonderful, as it means that we no longer need to do the hash merge to bring in default ‘params’.

But you will have likely read about that elsewhere.

The thing that I was happy to discover was the “named params” are available for Proc and lambda.

This means that we can now do something like this:

my_proc = Proc.new do |name: 'Joe', age: 23, **other_params|
  [name, age, other_params]
end

If you were to pass nothing at all to the Proc, you would get this: ["Joe", 23, {}]

Let’s see what happens if you change the name, and give it a some undetermined parameter:

my_proc = Proc.new do |name: 'Joe', age: 42, **other_params|
  [name, age, other_params]
end

my_proc[age: 49, hobbies: ['long walks', 'candlelight dinners', 'romantic comedies']]

We would end up with this as a return:

["Joe", 49, {:hobbies=>["long walks", "candlelight dinners", "romantic comedies"]}]

Compared to the extra work we would have had to do to get this in Ruby 1.9, I like it.

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