adornable

Use decorators on Ruby methods!

kjleitz
254
6
Ruby

Adornable

Adornable provides the ability to cleanly decorate methods in Ruby. You can make and use your own decorators, and you can also use some of the built-in ones that the gem provides. Decorating methods is as simple as slapping a decorate :some_decorator above your method definition. Defining decorators can be as simple as defining a method that yields to a block, or as complex as manipulating the decorated method’s receiver and arguments, and/or changing the functionality of the decorator based on custom options supplied to it when initially applying the decorator.

Installation

NOTE: This library is tested with Ruby versions 2.5.x through 3.2.x.

Locally (to your application)

Add the gem to your application’s Gemfile:

gem 'adornable'

…and then run:

bundle install

Globally (to your system)

Alternatively, install it globally:

gem install adornable

Usage

The basics

Think of a decorator as if it’s just a wrapper function. You want something to happen before, around, or after a method is called, in a reusable (but dynamic) way? Maybe you want to print to a log whenever a certain method is called, or memoize its result so that additional calls don’t have to re-execute the body of the method. You’ve tried this:

class RandomValueGenerator
  def value
    # logging the method call
    puts "Calling method `RandomValueGenerator#value` with no arguments"
    # memoizing the result
    @value ||= rand
  end

  def values(max)
    # logging the method call
    puts "Calling method `RandomValueGenerator#values` with arguments `[#{max}]`"
    # memoizing the result
    @values ||= {}
    @values[max] ||= (1..max).map { rand }
  end
end

random_value_generator = RandomValueGenerator.new

values1 = random_value_generator.values(1000)
# Calling method `RandomValueGenerator#values` with arguments `[1000]`
#=> [0.7044444114998132, 0.401953296596267, 0.3023797513191562, ...]

values1 = random_value_generator.values(1000)
# Calling method `RandomValueGenerator#values` with arguments `[1000]`
#=> [0.7044444114998132, 0.401953296596267, 0.3023797513191562, ...]

values3 = random_value_generator.values(5000)
# Calling method `RandomValueGenerator#values` with arguments `[5000]`
#=> [0.9916088057511011, 0.04466750434972333, 0.6073659341272127]

value1 = random_value_generator.value
# Calling method `RandomValueGenerator#value` with no arguments
#=> 0.4196007135344746

value2 = random_value_generator.value
# Calling method `RandomValueGenerator#value` with no arguments
#=> 0.4196007135344746

However, you have a million more methods to write, and if you refactor, you’ll have to screw around with a slew of method definitions across your app.

What if you could do this, instead, to achieve the same result?

class RandomValueGenerator
  extend Adornable

  decorate :log
  decorate :memoize
  def value
    rand
  end

  decorate :log
  decorate :memoize
  def values(max)
    (1..max).map { rand }
  end
end

Nice, right?

Note: in the case of multiple decorators decorating a method, each is executed from top to bottom.

Adding decorator functionality

Add the ::decorate macro to your classes by extend-ing Adornable:

class Foo
  extend Adornable

  # ...
end

Decorating methods

Use the decorate macro to decorate methods.

Using built-in decorators

There are a couple of built-in decorators for common use-cases (these can be overridden if you so choose):

class Foo
  extend Adornable

  decorate :log
  def some_method
    # the method name (Foo#some_method) and arguments will be logged
  end

  decorate :memoize
  def some_other_method
    # the return value will be cached
  end

  decorate :memoize
  def yet_another_method(some_arg, some_other_arg = true, key_word_arg:, key_word_arg_with_default: 123)
    # the return value will be cached based on the arguments the method receives
  end

  decorate :log
  decorate :memoize, for_any_arguments: true
  def oh_boy_another_method(some_arg, some_other_arg = true, key_word_arg:, key_word_arg_with_default: 123)
    # the method name (Foo#oh_boy_another_method) and arguments will be logged
    # the return value will be cached regardless of the arguments received
  end

  decorate :log
  def self.yeah_it_works_on_class_methods_too
    # the method name (Foo::yeah_it_works_on_class_methods_too) and arguments
    # will be logged
  end
end
  • decorate :log logs the method name and any passed arguments to the console
  • decorate :memoize caches the result of the first call and returns that initial result (and does not execute the method again) for any additional calls. By default, it namespaces the cache by the arguments passed to the method, so it will re-compute only if the arguments change; if the arguments are the same as any previous time the method was called, it will return the cached result instead.
    • pass the for_any_arguments: true option (e.g., decorate :memoize, for_any_arguments: true) to ignore the arguments in the caching process and simply memoize the result no matter what
    • a nil value returned from a memoized method will still be cached like any other value

Note: in the case of multiple decorators decorating a method, each is executed from top to bottom.

Writing custom decorators and using them explicitly

You can reference any decorator method you write, like so:

class FooDecorators
  # Note: this is defined as a CLASS method, but it can be applied to both class
  #       and instance methods. The only difference is in how you source the
  #       decorator when doing the decoration; see below for more info.
  def self.blast_it(context)
    puts "Blasting it!"
    value = yield
    "#{value}!"
  end

  # Note: this is defined as an INSTANCE method, but it can be applied to both
  #       class and instance methods. The only difference is in how you source
  #       the decorator when doing the decoration; see below for more info.
  def wait_for_it(context, dot_count: 3)
    ellipsis = dot_count.times.map { '.' }.join
    puts "Waiting for it#{ellipsis}"
    value = yield
    "#{value}#{ellipsis}"
  end
end

class Foo
  extend Adornable

  # Note: `from: FooDecorators` references a class (and will look for the
  #       `::blast_it` method on that class)
  decorate :blast_it, from: FooDecorators
  def some_method
    "haha I'm a method"
  end

  # Note: `from: FooDecorators.new` references an instance (and will look for
  #       the `#wait_for_it` method on that instance)
  decorate :wait_for_it, from: FooDecorators.new
  def other_method
    "haha I'm another method"
  end

  decorate :log
  def yet_another_method(foo, bar:)
    "haha I'm yet another method"
  end
end

foo = Foo.new

foo.some_method
#=> "haha I'm a method!" # Note the exclamation mark

foo.other_method
#=> "haha I'm another method..." # Note the ellipsis

foo.yet_another_method(123, bloop: "bleep")
# Calling method `Foo#yet_another_method` with arguments `[123, {:bloop=>"bleep"}]`
#=> "haha I'm yet another method"

Use the from: option to specify what should receive the decorator method. Keep in mind that the decorator method will be called on the thing specified by from:… so, if you provide a class, it better be a class method on that thing, and if you supply an instance, it better be an instance method on that thing.

Every custom decorator method that you define must take one required argument (context) and any number of keyword arguments. It should also yield (or take a block argument and invoke it) at some point in the body of the method. The point at which you yield will be the point at which the decorated method will execute (or, if there are multiple decorators on the method, each following decorator will be invoked until the decorators have been exhausted and the decorated method is finally executed).

The required argument (context)

The required argument is an instance of Adornable::Context, which has some useful information about the decorated method being called

  • Adornable::Context#method_name: the name of the decorated method being called (a symbol; e.g., :some_method or :other_method)
  • Adornable::Context#method_receiver: the actual object that the decorated method (the #method_name) belongs to/is being called on (an object/class; e.g., the class Foo if it’s a decorated class method, or an instance of Foo if it’s a decorated instance method)
  • Adornable::Context#method_arguments: an array of arguments passed to the decorated method, including keyword arguments as a final hash (e.g., if :yet_another_method was called like Foo.new.yet_another_method(123, bar: true, baz: 456) then method_arguments would be [123, {:bar=>true,:baz=>456}])
  • Adornable::Context#method_positional_args: an array of just the positional arguments passed to the decorated method, excluding keyword arguments (e.g., if :yet_another_method was called like Foo.new.yet_another_method(123, bar: true, baz: 456) then method_positional_args would be [123])
  • Adornable::Context#method_kwargs: a hash of just the keyword arguments passed to the decorated method (e.g., if :yet_another_method was called like Foo.new.yet_another_method(123, { bam: "hi" }, bar: true, baz: 456) then method_kwargs would be {:bar=>true,:baz=>456})
Custom keyword arguments (optional)

The optional keyword arguments are any parameters you want to be able to pass to the decorator method when decorating a method with ::decorate:

  • If you define a decorator like def self.some_decorator(context) then it takes no options when it is used: decorate :some_decorator.
  • If you define a decorator like def self.some_decorator(context, some_option:) then it takes one required keyword argument when it is used: decorate :some_decorator, some_option: 123 (so that ::some_decorator will receive 123 as the some_option parameter every time the decorated method is called). You can customize functionality of the decorator this way.
  • Similarly, if you define a decorator like def self.some_decorator(context, some_option: 456), then it takes one optional keyword argument when it is used: decorate :some_decorator is valid (and implies some_option: 456 since it has a default), and decorate :some_decorator, some_option: 789 is valid as well.
Yielding to the next decorator/decorated method

Every decorator method should also probably yield at some point in the method body. I say “should” because, technically, you don’t have to, but if you don’t then the original method will never be called. That’s a valid use-case, but 99% of the time you’re gonna want to yield.

Note: the return value of your decorator will replace the return value of the decorated method, so also you should probably return whatever value yield returned. Again, it is a valid use case to return something else, but 99% of the time you probably want to return the value returned by the wrapped method.

A contrived example of when you might want to muck around with the return value:

class FooDecorators
  def self.coerce_to_int(context)
    value = yield
    new_value = value.strip.to_i
    puts "New value: #{value.inspect} (class: #{value.class})"
    new_value
  end
end

class Foo
  extend Adornable

  decorate :coerce_to_int, from: FooDecorators
  def get_number_from_user
    print "Enter a number: "
    value = gets
    puts "Value: #{value.inspect} (class: #{value.class})"
    value
  end
end

foo = Foo.new

foo.get_number_from_user
# Enter a number
# > 123
# Value: "123" (class: String)
# New value: 123 (class: Integer)
#=> 123

Writing custom decorators and using them implicitly

You can also register decorator receivers so that you don’t have to reference them with the from: option:

class FooDecorators
  def self.blast_it(context)
    puts "Blasting it!"
    value = yield
    "#{value}!"
  end
end

class MoreFooDecorators
  def wait_for_it(context, dot_count: 3)
    ellipsis = dot_count.times.map { '.' }.join
    puts "Waiting for it#{ellipsis}"
    value = yield
    "#{value}#{ellipsis}"
  end
end

class Foo
  extend Adornable

  add_decorators_from FooDecorators
  add_decorators_from MoreFooDecorators.new

  decorate :blast_it
  decorate :wait_for_it, dot_count: 9
  def some_method
    "haha I'm a method"
  end
end

foo = Foo.new

foo.some_method
# Blasting it!
# Waiting for it.........
#=> "haha I'm a method!........."

Note: All the rest of the stuff from the previous section (using decorators explicitly) also applies here (using decorators implicitly).

Note: In the case of duplicate decorator methods, later receivers registered with ::add_decorators_from will override any decorators by the same name from earlier registered receivers.

Note: in the case of multiple decorators decorating a method, each is executed from top to bottom; i.e., the top wraps the next, which wraps the next, and so on, until the method itself is wrapped.

Development

Install dependencies

bin/setup

Run the tests

rake spec

Run the linter

rubocop

Contributing

Bug reports and pull requests for this project are welcome at its GitHub page. If you choose to contribute, please be nice so I don’t have to run out of bubblegum, etc.

License

This project is open source, under the terms of the MIT license.