Ruby passing symbol(s) as keyword argument(s)?-CodePudding

I have a method, where I want to use keyword parameter(s) and case/when statements, where I prefered to use symbols:

  def navigate_to(page:)
    case page
    when :inbox
      # some code
    when :archive
      # some code
    else
      # some code
    end
  end

Is this the correct syntax when calling the method?

navigate_to page: :inbox

The : : seems a little bit strange.

CodePudding user response：

The keyword argument syntax is:

key: value

If key is page and value is the symbol :inbox, you indeed have:

page: :inbox

You could also use a positional argument instead:

def navigate_to(page)
  # same as your code
end

navigate_to :inbox

CodePudding user response：

Yes, the correct syntax is navigate_to page: :inbox.

While this is common Ruby, it is short and equivalent for several different things. First, the braces.

You are actually calling:

navigate_to(page: :inbox)

Second, the keyword argument pattern originates from hashes as arguments. Before there were keyword arguments, a common way would be to pass in a hash[1], like so:

def navigate_to(options)
  page = options[:page]
end
navigate_to({ page: :inbox })

But when last argument in a method call is a hash, one can leave out the {}.

And last, the actual keys in the hash. A while ago (1.8 -> 1.9 IIRC) a short version was introduced for the following:

{ :page => 'Some Value' }, namely { page: 'Some Value' }. When Some Value is a symbol, that becomes { page: :inbox }.

So, taking all that:

navigate_to page: :inbox

Orignates from:

navigate_to({ :page => :inbox })

It might make more sense reading it like this, or knowing it comes from that.

And I know Ruby, nor ruby-ist, like braces, (), as can be seen in the mindboggling DSL of for example rspec, but I can advise especially new developers, to add them. It often makes code better understandable.

navigate_to(page: :inbox) is probably easier to understand than navigate_to page: :inbox, especially when you start calling through other methods: navigate_to page page_from_session :user.

[1] But, to stress, that is not really what is happening here. Keyword arguments and hash arguments do differ, now that we have keyword arguments. this just shows why the syntax is this way.