Access class from inside included module - ruby

I want to be able to do this:
class IncludingClass
include IncludedModule
end
module IncludedModule
self.parent_class # => IncludingClass, I wish
end
Any ideas? Sorry for the brevity. Typing this on a phone. At any rate, I've looked around and haven't been able to find this, which seems surprising for such a met aprogrammable language.

I don't believe modules keep track of what included them. But they do fire a MyModule.included(SomeClass) method as a callback when they get included, so you can keep track yourself.
module IncludedModule
# Array to store included classes
##included_classes = []
# Called when this module is included.
# The including class is passed as an argument.
def self.included(base)
##included_classes << base
end
# Getter for class variable
def self.included_classes
##included_classes
end
end
# Include the module
class IncludingClass
include IncludedModule
end
# Ask the module what included it.
puts IncludedModule.included_classes #=> [IncludingClass]
There's probably also a way to crawl all Classes declared and ask them what they included via SomeClass.included_modules but that's kind of hairy, and would be much slower.

Related

Defining nested classes both directly and via include

Suppose I'm modelling my home storage system. I have a bunch of different types of Container, and I've found that so many of them have ornaments in or on them that I've set up a bit of helper code for that common case.
Among my containers are my Mantlepiece and my Bookcase. I only store ornaments on the former; while the latter has all of ornaments, and hardback and softback books.
Here's an initial attempt:
module Properties
def has_ornament
include OrnamentThings
end
module OrnamentThings
module Things
class Ornament
end
end
end
end
class Container
extend Properties
end
class Mantlepiece < Container
has_ornament
end
class Bookcase < Container
has_ornament
module Things
class Hardback
end
class Paperback
end
end
end
[Mantlepiece, Bookcase].each do |place|
puts place.name
puts place.constants.inspect
puts place::Things.constants.inspect
end
# Output:
# Mantlepiece
# [:Things]
# [:Ornament]
# Bookcase
# [:Things]
# [:Hardback, :Paperback]
You can see that the Mantlepiece correctly nests Mantlepiece::Things::Ornament; but the in-class declaration of Things for Bookcase means that Bookcase::Things only nests Hardback and Paperback. Bookcase::Things::Ornament is missing.
Can I write this neatly so that Bookcase can call has_ornament, then declare its own set of Things, and have all of them nested in the same namespace?
Even though your mantlepiece and bookcase both have things, those things are different (because they contain different classes). So they can't just include some common Things module; they instead have to define their own separate Things, just like you did in Bookcase by declaring module Things.
def has_ornament
const_set(:Things, Module.new) unless const_defined? :Things, false
self::Things.include OrnamentThings
end
module OrnamentThings
class Ornament
end
end
This works because Ruby lets you reopen modules using the same syntax you use to declare them. has_ornament defines a brand new Things module, which you then open to add more things. If you call has_ornament after your custom things it instead skips the creation and adds to the module you made (the false makes sure we're looking for Things only in the current class).

How does include Module work?

module A
end
class Klass
include A
end
How does this include influence Klass? Does it simply put Klass into module A or do something more?
Short Answer: If you have some methods inside your module and you use include in a class, those methods can be used in the class.
Module A
def shout
puts "HEY THERE!!!!"
end
end
class Klass
include A
end
# Create instance of Klass
instance = Klass.new
# Produces "HEY THERE!!!!"
instance.shout
The include method takes all the methods from another module and
includes them into the current module. This is a language-level thing
as opposed to a file-level thing as with require. The include method
is the primary way to "extend" classes with other modules (usually
referred to as mix-ins). For example, if your class defines the method
"each", you can include the mixin module Enumerable and it can act as
a collection. This can be confusing as the include verb is used very
differently in other languages.
from here: What is the difference between include and require in Ruby?
also take a look at this page: http://www.ruby-doc.org/docs/ProgrammingRuby/html/tut_modules.html it has a verbose explanation about how include works.
include is one of the ways to include methods of a Module in another Module or Class.
Please read my article on how that affects method calls in Ruby/

Allowing users to create plugins for my class, how to extend it correctly?

I have a class which I want other developers to be able to create modules to extend my class and give it more instance variables.
How can I automatically include modules in my class based on files in a particular folder? i.e. load all files and include them as modules for my class
How can I do this and somehow avoid method naming collisions?
I was thinking I could pass the name of the plugin in the initialize method, and do this:
class MyClass
def initialize(plugin_name=nil)
end
def method_missing(method_name)
"#{plugin_name}".send(method_name)
end
end
Would something like this work in theory, please help out in the method_missing as I have never written one before. I'm trying to basically specify a particular plugin name to avoid any name collisions.
Or should I, when including the plugins, output an error if there is a method collision?
Allowing external code to be melted in your class sounds dangerous and drives into names collisions as you guessed. It cans also drive into unexpected behavior, since you allow external code to mess with your class internals.
The best way to handle a plugin would be to encaspulate the behavior that would be replaced.
Let's take an example :
Given you're building a Logger, we can imagine that you can create plugins to specify where the logs will be wrote.
You can then create the following class :
class Logger
def initialize(store)
#store = store
end
def info(message)
#store.write(:info, message)
end
end
class StandardOutputStore
def write(level, message)
puts "#{level}: #{message}"
end
end
class FileStore
def initalize(filename)
#filename = filename
end
def write(level, message)
File.open(#filename, "a") do |file|
file.write("#{level}: #{message}")
end
end
end
Then you can you instanciate the right plugin this way :
logger = Logger.new(StandardOutputStore.new)
logger.warn "hello"
logger = Logger.new(FileStore.new("/tmp/log"))
logger.warn "hello"
This way of doing things provides modularity, more flexibility and is more solid than overloading things in your class with external code.
Loading modules as they are found in a directory is a matter of toying with Dir.glob and require. To explore what had been found under your plugin directory, you can force your users to write plugins in a module, like Foo::Plugins::FileStore and inspect which constants are present in the Foo::Plugins module after requiring the files. See http://www.ruby-doc.org/core-1.9.3/Module.html#method-i-constants for more informations.
Edit: As you don't have any interface to map to since you provides the methods to an ERB template, you could do the following :
Plugins are in the following form :
module Plugins
module Emoticons
def smile
":-)"
end
end
end
You can then load them with the following :
Dir["/plugins/*.rb"].each {|file| require file }
And include them, given TemplateMethods is a module included in the context of your ERB template.
Plugins.constants.each do |constant|
mod = Plugins.const_get constant
TemplateMethods.send(:include, mod)
end
Using send isn't very elegant, I'd suggest building a class method on TemplateMethods that encapsulate the whole thing, like TemplateMethods.load_plugins_method! The bang here would warn about the intrusive action done by the dynamic modules inclusion.
That should do the job :)

When are modules included in a Ruby class running in rails?

I'm trying to write a method that tells me every class that includes a particular Module. It looks like this -
def Rating.rateable_objects
rateable_objects = []
ObjectSpace.each_object(Class) do |c|
next unless c.include? Rateable
rateable_objects << c
end
rateable_objects
end
Where "Rateable" is my module that I'm including in several models.
What i'm finding is that this method return [] if i call it immediately after booting rails console or running the server. But if i first instantiate an instance of one of the consuming models it will return that model in the result.
So when do modules get included? I'm guessing later in the process than when he app starts up. If i can't get this information this way early in the process, is there anyway to accomplish this?
They are included when the include statement is executed when the class is defined. Rails autoloads modules/classes when you first use them. Also, you might try something like this:
module Rateable
#rateable_object = []
def self.included(klass)
#rateable_objects << klass
end
def rateable_objects
#rateable_objects
end
end
This will build the list as classes include the module.

Test modules with Test::Unit

I encountered a problem when trying to test a module with Test::Unit. What I used to do is this:
my_module.rb:
class MyModule
def my_func
5 # return some value
end
end
test_my_module.rb:
require 'test/unit'
require 'my_module'
class TestMyModule < Unit::Test::TestCase
include MyModule
def test_my_func
assert_equal(5, my_func) # test the output value given the input params
end
end
Now the problem is, if my_module declares an initialize method, it gets included in the test class and this causes a bunch of problems since Test::Unit seems to override/generate an initialize method. So I'm wondering what is the best way to test a module?
I'm also wondering wether my module should become a class at this point since the initialize method is made for initializing the state of something. Opinions?
Thanks in advance !
Including an initialize method in a module feels very wrong to me, so I'd rethink that at the very least.
To answer your question about testing this as a module more directly, though, I would create a new, empty class, include your module in it, create an instance of that class, and then test against that instance:
class TestClass
include MyModule
end
class TestMyModule < Unit::Test::TestCase
def setup
#instance = TestClass.new
end
def test_my_func
assert_equal(5, #instance.my_func) # test the output value given the input params
end
end
Yeah, your initialize should definitely suggest that you're going towards a class. A module in ruby often feels like an interface in other languages, as long as you implement some basic things when you include the module you'll get a lot for free.
Enumerable is a great example, as long as you define [] and each when you include Enumerable you suddenly get pop, push, etc.
So my gut feeling about testing modules is that you should probably be testing classes that include the module rather than testing the module itself unless the module is designed to not be included in anything, it's simply a code storage mechanism.

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