Necklace

Ports the -> macro from Clojure to make long chains of Enumerable more readable

Usually when chaining method calls in ruby, the names of the methods are descriptive and the chain is readable. (Note that this may violate the Law of Demeter, but this is simply an example). One can imagine something like

food_processor.add(vinegar)
              .add(garlic)
              .add(pepper)
              .start
              .drizzle(oil)

Where each method returns self and the chain describes the actions.

However, with Enumerable, because the methods are more abstract, readability is often sacrificed when chaining operations:

[1, 3, 5, 7, 9].map do |n|
  n + 1
end.map do |n|
  n * 2
end.map |n|
  n - 3
end.select |n|
  n.even?
end

Two possible solutions are to name only the inner methods:

[1, 3, 5, 7, 9].map do |n|
  increment(n)
end.map do |n|
  double(n)
end.map |n|
  subtract(n, 3)
end.select |n|
  n.even?
end

or extract each transformation in a method and call them inside-out - lisp-style:

even(
  subtract_three(
    double(
      incrememnt([1, 3, 5, 7, 9])
    )
  )
)

This last looks a lot like a lisp, and Clojure has a macro to make calls like this easier to read:

(-> [1, 3, 5, 7, 9]
  increment
  double
  subtract_three
  even
)

Necklace attempts to replicate at least some aspects of the Clojure threading macros (->, ->>) in ruby so that long chains of enumerable transformations can be called without sacrificing readablility.

simply include Necklace in a class

Then define methods that take each successive result as their argument.

Then call through with the enumerable as the first argument and an array of symbols corresponding to the method names as the second argument.

through([1, 3, 5, 7, 9],
        [:increment,
         :double,
         :subtract_three,
         :even
        ]
)

For methods that have multiple arguments, both a through_first and through_last method are provided. These thread the enumerable as the first or last argument of the method calls respectively. Methods with arguments in addition to the enumerable have the method and it's additional arguments packaged in an array:

through_first([1, 3, 5, 7, 9],
              [[:add_to_each, 3]
               :double
              ]
             )

will call

add_to_each([1, 3, 5, 7, 9], 3)

and

through_last([1, 3, 5, 7, 9],
             [[:add_to_each, 3]
              :double
             ]
            )

will call

add_to_each(3, [1, 3, 5, 7, 9])

Copyright (c) 2015 Stuart Terrett

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