Organizing monkey patches - ruby

I read a blog post that recommends namespacing your monkey patches so they can be easily viewed and included.
For example:
module CoreExtensions
module DateTime
module BusinessDays
def weekday?
!sunday? && !saturday?
end
end
end
end
Would go in the: lib/core_extensions/class_name/group.rb file.
It can be included in the DateTime class with the Module#include instance method (which a class inherits because a Class is a Module)
# Actually monkey-patch DateTime
DateTime.include CoreExtensions::DateTime::BusinessDays
My question is where do the include statements go? Is there a convention?
For example:
I have the following monkey patches:
# http://www.justinweiss.com/articles/3-ways-to-monkey-patch-without-making-a-mess/
module CoreExtensions
module String
module Cases
def snakecase
return self if self !~ /[A-Z]+.*/
# http://rubular.com/r/afGWPWLRBB
underscored = gsub(/(.)([A-Z])/, '\1_\2')
underscored.downcase
end
def camelcase
return self if self !~ /_/ && self =~ /[A-Z]+.*/
split('_').map{ |e| e.capitalize }.join
end
end
end
end
That live inside the lib/core_extensions/string/cases.rb file.
Where should I put my String.include CoreExtensions::String::Cases statement?
Also to be clear this is just a ruby project, does that make a difference?
I've tried putting it inside lib/devify.rb
require 'devify/version'
require 'devify/some_dir'
require 'devify/scaffold'
require 'devify/tree_cloner'
require 'devify/renderer'
require 'devify/project'
require 'devify/tasks/some_task'
require 'devify/tasks/bootstrap'
require 'core_extensions/string/cases'
module Devify
String.include CoreExtensions::String::Cases
end
This works and it makes sense why it works. It's because my entire app lives inside the Devify module or namespace.
This way is also good because I'm not polluting the global namespace correct? Because I'm only monkey patching Strings that live inside Devify?
Just not sure not if this is the right way to go about it.

It doesn't matter where you put the include call.
Calling String.include will always monkey patch the one String class that is used by all the strings in the entire object space. So best put the instruction at the top level as to not mislead readers of the code.
Monkey patching is always global.
It is a powerful feature and can be used for good.
If you are authoring a gem be aware that you're sharing a global namespace with others. The same is also true for top-level modules and even the gem name though. Shared namespaces are just a reality of shared code.
If you are looking for lexically scoped monkey patches look into the new refinement feature that was introduce with Ruby 2.
Refinements are an idea taken from Smalltalk's class boxes. Refinements are not without their own issues though, for example they lack support for introspection and reflection. Thus essentially making them stealth and unfit for production use.
If you are looking to limit the monkey patches to some string object only, consider either subclassing String or calling extend on an instance.

Although ruby offers many ways of changing the content of a class or a method dynamically, the monkey patching can lead to big problems and strange bugs. I read this post (http://www.virtuouscode.com/2008/02/23/why-monkeypatching-is-destroying-ruby/) about why it´s a bad idea to use monkey-patching.
In summary, many things that he says make sense. When you create a monkey-patching, you are assuming that it will only works at that project, and, maybe you can create collisions and unprevisible side-effects when more libraries with similar purposes are put together.
There are cases where the benefits of the monkey-patching were awesome, like ActiveSupport way of dealing with dates manipulation by monkey-patching the Fixnum class with the ago or from_now methods, or as the method to_json. However, monkey patching should be avoided.
The point is: Ruby is an object-oriented language, and you can achieve your objectives using object composition, or any other patterns. Monkey-patching, at some way, leads you in the opposite direction of object oriented philosophy, since you add more responsibilities to an pre-existent class and increases it's public interface to serve a new funcionallity.
Besides, it's not explicit the behavior of that class and the public methods available. You cannot know, by looking at the class definition, what it makes and what is it's role at the system, and how it interact with other objects. It makes a simple task much more harder at the end.
Monkey patching makes everything much more smaller and simpler, apparently, but avoiding it makes your code much more maintanable, easier to debug, read and test, and much more elegant, since it is compliant to the "OOP" patterns.

Related

Monkey patching built-in ruby classes in limited scopes

I'm working on an internal Ruby DSL and to make it look as pretty as possible I need to monkey patch the Symbol class and add some operators. I want to be responsible in how I do this and would like to limit the scope and lifetime of the patches to a specific block of code. Is there a standard pattern for doing this? Here's some pseudo-code to show what I'm thinking:
class SomeContext
def self.monkey_patch_region(&block)
context = SomeContext.new
context.monkey_patch_Symbol
context.instance_eval(&block)
context.unmonkey_patch_Symbol
end
# magical method
def monkey_patch_Symbol
#...
end
# another magical method
def unmonkey_patch_Symbol
#...
end
end
I believe, that you're looking for ruby refinements. The feature has landed in ruby trunk, but it might be reverted before 2.0
I've heard about mixology gem. It was designed to mixin and unmix modules. Maybe it can be useful to monkey and unmonkey patches.
UPDATE: mixology won't help you, as it (un)mixes modules to objects (as with extend), not to classes (as with include), and you want monkey/unmonkey core classes, not their objects individually. Anyway I intend to maintain this answer as possibly useful reference for someone else.

ruby module_function vs including module

In ruby, I understand that module functions can be made available without mixing in the module by using module_function as shown here. I can see how this is useful so you can use the function without mixing in the module.
module MyModule
def do_something
puts "hello world"
end
module_function :do_something
end
My question is though why you might want to have the function defined both of these ways.
Why not just have
def MyModule.do_something
OR
def do_something
In what kind of cases would it be useful to have the function available to be mixed in, or to be used as a static method?
Think of Enumerable.
This is the perfect example of when you need to include it in a module. If your class defines #each, you get a lot of goodness just by including a module (#map, #select, etc.). This is the only case when I use modules as mixins - when the module provides functionality in terms of a few methods, defined in the class you include the module it. I can argue that this should be the only case in general.
As for defining "static" methods, a better approach would be:
module MyModule
def self.do_something
end
end
You don't really need to call #module_function. I think it is just weird legacy stuff.
You can even do this:
module MyModule
extend self
def do_something
end
end
...but it won't work well if you also want to include the module somewhere. I suggest avoiding it until you learn the subtleties of the Ruby metaprogramming.
Finally, if you just do:
def do_something
end
...it will not end up as a global function, but as a private method on Object (there are no functions in Ruby, just methods). There are two downsides. First, you don't have namespacing - if you define another function with the same name, it's the one that gets evaluated later that you get. Second, if you have functionality implemented in terms of #method_missing, having a private method in Object will shadow it. And finally, monkey patching Object is just evil business :)
EDIT:
module_function can be used in a way similar to private:
module Something
def foo
puts 'foo'
end
module_function
def bar
puts 'bar'
end
end
That way, you can call Something.bar, but not not Something.foo. If you define any other methods after this call to module_function, they would also be available without mixing in.
I don't like it for two reasons, though. First, modules that are both mixed in and have "static" methods sound a bit dodgy. There might be valid cases, but it won't be that often. As I said, I prefer either to use a module as a namespace or mix it in, but not both.
Second, in this example, bar would also be available to classes/modules that mix in Something. I'm not sure when this is desirable, since either the method uses self and it has to be mixed in, or doesn't and then it does not need to be mixed in.
I think using module_function without passing the name of the method is used quite more often than with. Same goes for private and protected.
It's a good way for a Ruby library to offer functionality that does not use (much) internal state. So if you (e.g.) want to offer a sin function and don't want to pollute the "global" (Object) namespace, you can define it as class method under a constant (Math).
However, an app developer, who wants to write a mathematical application, might need sin every two lines. If the method is also an instance method, she can just include the Math (or My::Awesome::Nested::Library) module and can now directly call sin (stdlib example).
It's really about making a library more comfortable for its users. They can choose themself, if they want the functionality of your library on the top level.
By the way, you can achieve a similar functionality like module_function by using: extend self (in the first line of the module). To my mind, it looks better and makes things a bit clearer to understand.
Update: More background info in this blog article.
If you want to look at a working example, check out the chronic gem:
https://github.com/mojombo/chronic/blob/master/lib/chronic/handlers.rb
and Handlers is being included in the Parser class here:
https://github.com/mojombo/chronic/blob/master/lib/chronic/parser.rb
He's using module_function to send the methods from Handlers to specific instances of Handler using that instance's invoke method.

"Interfaces & Abstract Classes unnecessary in Ruby" --> Can someone explain?

I'm trying to wrap my head around Ruby, and one thing I'm struggling with is the lack of interface/abstract class support. From googling about, the response I continuously see to abstract class related Ruby questions is "You're thinking in Java. Ruby doesn't work that way"
So, how would one work in Ruby without interfaces/abstract classes?
For example, in Java I might create an abstract class "book", with subclasses "novel", "textbook", and "journal". There is a lot of common functionality that I throw in 'book', but I don't want it to be directly accessible - a book must be either a novel, textbook or journal.
In ruby, how would I write out that sort of functionality?
I am also Ruby starter. From my understanding, there is a closer rival for abstract classes in ruby. that is module. you can't create any instances of module but you can include with another class. So a target class will get the whole functionality of parent
module Log
def write
//blah
end
end
class EventLog
include Log
def Prepare
end
end
In statically typed languages like java/C# , Interfaces enforce the classes to have all the methods at compile time. Since Ruby is dynamic, there is no meaning in it.
For more clarity, check these posts why dynamic languages don't require interfaces..
why-dont-we-require-interfaces-in-dynamic-languages
why-do-dynamic-languages-like-ruby-and-python-not-have-the-concept-of-interfaces
Cheers
there are ways to implement this type of thing, including abstract_type gem. While ruby doesn't require it and has mixins, i think there are cases, like adapters, where you'd want to secure your interface to a set of objects with something more explicit.
also, check out http://metabates.com/2011/02/07/building-interfaces-and-abstract-classes-in-ruby/

ruby oo design question should i reopen the class or use extension pattern

so I have an ruby object that i need to create as a pdf and excel row and cvs row
so far I've created a new class with a method to take in the object and do the necessary stuff to produce the pdf , excel , csv
I've been reading Agile Software Development, Principles, Patterns, and Practices and it mentioned the extension method so i was going to do but since this is ruby should i just be reopening the class in the another file and added the methods on there to separate them from the main class
so
file ruby_model.rb
class RubyModel < ActiveRecord::Base
end
then do
ruby_model_pdf.rb
class RubyModel
def to_pdf
end
end
ruby_model_cvs.rb
class RubyModel
def to_csv
end
end
or should i go with with the object extension pattern?
Cheers
You should put your methods in a module and include the module in the class. This way is preferable because it's easier to see where the methods came from (in a backtrace, for example), and it's easier to reuse the methods if it turns out that they can be used in other classes too.
For example:
module Conversions
def to_pdf
end
def to_csv
end
end
class RubyModel
include Conversions
end
It might also be a good idea to put to_pdf and to_csv in different modules, unless it's the case that if you want to mix in one you always want to mix in the other.
This all assumes that the methods don't belong in the class itself, but judging from the names they don't.
If the language feature works fine, then keep it simple and use it.
Design patterns are documented workarounds for cases where the language is not expressive enough. A Ruby example would be Iterator, which is made redundant by blocks and Enumerable.

What are some good examples of Mixins and or Traits?

I was reading up on Ruby, and learned about its mixins pattern, but couldn't think of many useful mixin functionality (because I'm not used to thinking that way most likely). So I was wondering what would be good examples of useful Mixin functionality?
Thanks
Edit: A bit of background. I'm Coming from C++, and other Object languages, but my doubt here is that Ruby says it's not inheriting mixins, but I keep seeing mixins as Multiple inheritance, so I fear I'm trying to categorize them too soon into my comfort zone, and not really grok what a mixin is.
They are usually used to add some form of standard functionality to a class, without having to redefine it all. You can probably think of them a bit like interfaces in Java, but instead of just defining a list of methods that need to be implemented, many of them will actually be implemented by including the module.
There are a few examples in the standard library:
Singleton - A module that can be mixed into any class to make it a singleton. The initialize method is made private, and an instance method added, which ensures that there is only ever one instance of that class in your application.
Comparable - If you include this module in a class, defining the <=> method, which compares the current instance with another object and says which is greater, is enough to provide <, <=, ==, >=, >, and between? methods.
Enumerable - By mixing in this module, and defining an each method, you get support for all the other related methods such as collect, inject, select, and reject. If it's also got the <=> method, then it will also support sort, min, and max.
DataMapper is also an interesting example of what can be done with a simple include statement, taking a standard class, and adding the ability to persist it to a data store.
Well the usual example I think is Persistence
module Persistence
def load sFileName
puts "load code to read #{sFileName} contents into my_data"
end
def save sFileName
puts "Uber code to persist #{#my_data} to #{sFileName}"
end
end
class BrandNewClass
include Persistence
attr :my_data
def data=(someData)
#my_data = someData
end
end
b = BrandNewClass.new
b.data = "My pwd"
b.save "MyFile.secret"
b.load "MyFile.secret"
Imagine the module is written by a Ruby ninja, which persists the state of your class to a file.
Now suppose I write a brand new class, I can reuse the functionality of persistence by mixing it in by saying include ModuleILike. You can even include modules at runtime. I get load and save methods for free by just mixing it in. These methods are just like the ones that you wrote yourself for your class. Code/Behavior/Functionality-reuse without inheritance!
So what you're doing is including methods to the method table for your class (not literally correct but close).
In ruby, the reason that Mixins aren't multiple-inheritance is that combining mixin methods is a one time thing. This wouldn't be such a big issue, except that Ruby's modules and classes are open to modification. This means that if you mixin a module to your class, then add a method to the module, the method will not be available to your class; where if you did it in the opposite order, it would.
It's like ordering an ice-cream cone. If you get chocolate sprinkles and toffee bits as your mixins, and walk away with your cone, what kind of ice cream cone you have won't change if someone adds multicolored sprinkles to the chocolate sprinkles bin back at the ice-cream shop. Your class, the ice cream cone, isn't modified when the mixin module, the bin of sprinkles is. The next person to use that mixin module will see the changes.
When you include a module in ruby, it calls Module#append_features on that module, which add a copy of that module's methods to the includer one time.
Multiple inheritance, as I understand it, is more like delegation. If your class doesn't know how to do something, it asks its parents. In an open-class environment, a class's parents may have been modified after the class was created.
It's like a RL parent-child relationship. Your mother might have learned how to juggle after you were born, but if someone asks you to juggle and you ask her to either: show you how (copy it when you need it) or do it for you (pure delegation), then she'll be able at that point, even though you were created before her ability to juggle was.
It's possible that you could modify a ruby module 'include' to act more like multiple inheritance by modifying Module#append_features to keep a list of includers, and then to update them using the method_added callback, but this would be a big shift from standard Ruby, and could cause major issues when working with others code. You might be better creating a Module#inherit method that called include and handled delegation as well.
As for a real world example, Enumerable is awesome. If you define #each and include Enumerable in your class, then that gives you access to a whole host of iterators, without you having to code each and every one.
It is largely used as one might use multiple inheritance in C++ or implementing interfaces in Java/C#. I'm not sure where your experience lies, but if you have done those things before, mixins are how you would do them in Ruby. It's a systemized way of injecting functionality into classes.

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