Created: 2008-03-18 19:58
Updated: 2019-01-28 10:14
License: mit



The Methodphitamine is a library for syntactically cleaner list comprehensions and an interesting approach to monads in Ruby.

For more information, read my blog post covering the Methodphitamine.

Cleaner Symbol#to_proc

One of the beautiful things the Ruby community has informally built into the language is Symbol#to_proc. The Methodphitamine takes beauty one step further.

Below are code examples which show the Methodphitamine's syntactical improvements over vanilla Ruby and Symbol#to_proc:

First, the pure-Ruby way:

User.find(:all).map{|x|{|y| y.last_name.capitalize }}

And now with Symbol#to_proc:


And now with the Methodphitamine once more:

User.find(:all).map &

Notice how even with Symbol#to_proc a block literal is still necessary because it simply can’t do nested arguments. The Methodphitamine fixes this by preserving all arguments and being more readable to boot.

New: Monads

You can now do something like this:

my_array.maybe &it.first.reverse.upcase

If the my_array variable were equal to ["foo", "bar", "qaz"], the result of the expression above would be "OOF". However, if my_array were equal to [], the result of the expression would be nil. This maybe method will execute the chain of methods if and only if all were successful. If one failed, nil is returned.

So how does The Methodphitamine work?

The it() and its() protected methods are added to Kernel so it can be called from anywhere in a Ruby script but not on any particular Object instance. They each simply return a new It instance.

The It class has all instance methods stripped from it (except the ones Ruby complains about) to ensure method_missing() catches everything. In the example [1,"2",3].map &, the It object first receives the class() method with no arguments via method_missing(). This gets enqueued in the @methods Array and it returns itself to receive any more methods. It then receives the next method, namely name(), and enqueues that alongside the previous method. When no more methods exist, Ruby determines if the It instance has a to_proc() method by calling respond_to?(:to_proc) so this has to be ignored and self suffices as a Ruby true boolean.

Then the magic happens. Because map() takes a block (essentially a Proc argument), this can be substituted with a variable or method that returns a block as long as an ampersand prepends it to let the Ruby interpreter know to call to_proc() on it. The It#to_proc() method is invoked, building a custom, dynamic Proc. Because these enumerations yield a variable, the dynamic Proc is executed for each item in the collection and obj consequentially becomes a reference to the current item in the collection. We then run through the enqueued methods with inject(), passing along the return value of executing each method in the order received with arguments intact. When inject() is done, it simply returns the grand product which becomes the return value of the Proc itself. Simple, right? :)

I chose to define both it() and its() since methods in Ruby can semantically either mean “the result of this action” or the possessive “this attribute.” For example, it.to_s and it.sort_by are both conceptual actions and and its.last are both conceptual attributes.

The idea of an it implied block argument comes from the Groovy guys. For example, this is valid Groovy:

[1,2,3,4].each { println it }

From the Groovy documentation on closures, “A closure always has at least one argument, which will be available within the body of the closure via the implicit parameter it if no explicit parameters are defined. The developer never has to declare the it variable – like the this parameter within objects, it is implicitly available.”

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