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.