Colon in arguments of a method call - Ruby

Question

when looking to some Ruby code I found the following method:

def connection
    unless @_mc_connection && valid? && @_ns_version == get_version
      @_mc_connection = ::Dalli::Client.new(self.dalli_servers, self.dalli_options.merge(namespace: namespace))
    end
    @_mc_connection
  end

My question is about the use of dalli_options.merge(namespace: namespace). What is the purpose of the colon here? Is an hash member?

Answer 1

What is the purpose of the colon here? Is an hash member?

Yes, it is a Hash object.

A Hash can be easily created by using its implicit form:

grades = { "Jane Doe" => 10, "Jim Doe" => 6 }

Hashes allow an alternate syntax form when your keys are always symbols. Instead of

options = { :font_size => 10, :font_family => "Arial" }

You could write it as:

options = { font_size: 10, font_family: "Arial" }

Answer 2

Depending on the Ruby version, this is either a Hash literal (1.9) or a keyword argument (2.0+).

Answer 3

The colon is part of the symbol syntax.

The following are equivalent:

namespace:   #only valid inside a hash

and

:namespace

With the former, the 'hash rocket' operator (=>) can be omitted (and usually is, for ease of reading).

However, this is only the case when your keys are symbols. If your keys are strings, as in

{ 'namespace' => 'api' }

the hash rocket is required.