Mastering Ruby Closures

Procs and the Four Ways of Calling Them

Unlike the language named after a certain serpent, Ruby embraces TMTOWTDI (pronounced as Tim Toady), or There’s more than one way to do it. The calling of Procs is a wonderful example. In fact, Ruby gives you four different ways:

1. Proc#call(args)

2. .(args)

3. Threequals

4. Lambdas

Fire up irb. Let’s begin by creating a very simple Proc:

>> p = proc { |x, y| x + y }
=> #<Proc:0x007ffb12907940@(irb):1>

There are two things to notice here. First, the return value tells you that a Proc has been created. Second, Ruby provides a shorthand to create Procs. This is really a method in the Kernel class:

>> p = Kernel.proc { |x, y| x + y }
=> #<Proc:0x007ffb12907940@(irb):1>

Of course, since Proc is ...