More natural way of Proc calling in Ruby 1.9

Question

As we know, there are several way of Proc calling in Ruby 1.9

 f =->n {[:hello, n]}
 p f[:ruby]       # => [:hello, :ruby]
 p f.call(:ruby)  # => [:hello, :ruby]
 p f.(:ruby)      # => [:hello, :ruby]
 p f === :ruby    # => [:hello, :ruby]

I am curious, what is more 'natural' way of calling Proc? 'Natural', probably, means more Computer Science - like way.

Answer 1

The second option is by far the most used.

p f.call(:ruby)  # => [:hello, :ruby]

It makes it more similar to a standard method. Also, some libraries actually rely on duck typing when validating arguments checking the availability of the #call method. In this case, using #call ensures you can provide a lambda or any other object (including a Class) that responds to #call.

Rack middlewares are a great example of this convention. The basic middleware can be a lambda, or you can supply more complex logic by using classes.

Answer 2

I always use option 3. Considering the syntactic ambiguities of being able to call methods without parentheses, this is the closest you can get to actual method call syntax.

Answer 3

I saw the first way used in Rack source code. It confused me in a long time. It's picked from lib/rack/builder.rb (version: 1.6.0.alpha)

module Rack
  class Builder
    ...

    def to_app
      app = @map ? generate_map(@run, @map) : @run
      fail "missing run or map statement" unless app

      # This is the first option calling a proc
      # @use is a array of procs (rack middleware)
      @use.reverse.inject(app) { |a,e| e[a] }
    end

    ...
  end
end