I'm trying to define a couple of modules to easily add in some instance and class methods to other classes, here's what I'm doing:
module Foo
module Bar
def speak
puts "hey there"
end
end
module Baz
extend Foo::Bar
def welcome
puts "welcome, this is an instance method"
end
end
end
class Talker
include Foo::Baz
end
Talker.new.welcome
Talker.speak
The output of this is:
welcome, this is an instance method
undefined method 'speak' for Talker.class (NoMethodError)
I was expecting Talker to have the 'speak' method since it includes Foo::Baz which itself extends Foo::Bar.
What am I missing?
You can try this:
module Baz
extend Foo::Bar
def self.included(base)
base.send :extend, Foo::Bar
end
def welcome
puts "welcome, this is an instance method"
end
end
This will auto-extend all classes in wich Baz is included.
PS:
extend Foo::Bar in module Baz was in original snippet, this code do not influence on method def self.included(base).
try this:
class Talker
extend Foo::Baz
end
since you want to call Talker.speak as a class method and not as an instance method (like Talker.new.speak) you have to include the Foo:Baz in a way that the class will take the methods itself.
One possibility is to use 'extend' (as above) the other is modifying it's eigenclass:
class Talker
class << self
include Foo::Baz
end
end
Related
I'd like my module to define new instance methods based on its including class' instance methods. But in the included hook, the class methods are not defined yet (as the module is included at the top of the class, before the class methods are defined):
module MyModule
def self.included(includer)
puts includer.instance_methods.include? :my_class_method # false <- Problem
end
end
class MyClass
include MyModule
def my_class_method
end
end
I want the users of the module to be free to include it at the top of their class.
Is there a way to make a module define additional methods to a class?
Note: I don't have to use the included hook if there is another way to achieve this.
There'a a method_added callback you could use:
module MyModule
def self.included(includer)
def includer.method_added(name)
puts "Method added #{name.inspect}"
end
end
end
class MyClass
include MyModule
def foo ; end
end
Output:
Method added :foo
If you want to track both, existing and future methods, you might need something like this:
module MyModule
def self.on_method(name)
puts "Method #{name.inspect}"
end
def self.included(includer)
includer.instance_methods(false).each do |name|
on_method(name)
end
def includer.method_added(name)
MyModule.on_method(name)
end
end
end
Example:
class MyClass
def foo ; end
include MyModule
def bar; end
end
# Method :foo
# Method :bar
I'm having some trouble understanding how to incorporate my own helper methods into a Ruby module.
My code:
module MyModule
def self.foo
bar
end
def bar
# helper for MyModule.foo
end
end
MyModule.foo
#=> NameError: undefined local variable or method `bar' for MyModule:Module
I'm not sure why MyModule cannot recognize the bar method. What aspect of scope in Ruby am I being oblivious to?
Modules can be integrated into classes as mixins. So, you need to include it in a class so it can be used with instance of that class.
As of now, you can make bar as your module method so it can be accessed as is.
module MyModule
def self.foo
bar
end
def self.bar
puts "Now it works"
end
end
MyModule.foo #=> Now it works
Ruby Docs
A Module is a collection of methods and constants. The methods in a
module may be instance methods or module methods. Instance methods
appear as methods in a class when the module is included, module
methods do not.
You are trying to call an instance method from a class method. You would have to write
module MyModule
def MyModule.foo
MyModule.bar
end
# Or you can have it this way
def MyModule::bar
# helper for MyModule.foo
end
end
MyModule.foo
to get what you want.
You're missing the scope of a method (module as well as instance) and basically it's lifecycle..
Module method way: -
Following is how you define the module with module methods.
module MyModule
def self.foo
puts "called self.foo"
bar
end
def self.bar
puts "self.bar got called"
# helper for MyModule.foo
end
end
Now, This way, you do not have to instantiate any object to call those methods.. Here is how you would call the methods (one inside the other)
MyModule.foo
Using a class to instantiate the Module and calling methods will not work as they are not instance methods.
Output -
called foo
bar got called
Instance method way: - Following is how you'll define the module with instance methods so that they will work between classes and objects..
module MyModule
def foo
puts "called foo"
bar
end
def bar
puts "bar got called"
# helper for MyModule.foo
end
end
class TestModule
include MyModule
end
Choosing to use the module methods this way you have to call the methods inside module as per below -
#instantiating module MyModule via class
myinstance = TestModule.new
myinstance.foo
Output -
called foo
bar got called
I have a module and would like to mixin some methods as class methods and some as instance methods.
For example:
module Foo
def self.class_method
end
def instance_method
end
end
class Bar
include Foo
end
Usage:
Bar.class_method
Bar.new.instance_method
Is it possible to do this in Ruby?
If not, is it possible to define which methods are class methods and which are instance methods within the Bar class?
I don't want the same method defined as both a class and instance method.
This pattern is very common in Ruby. So common, in fact, that ActiveSupport::Concern abstracts it a bit.
Your typical implementation looks like this:
module Foo
def self.included(other_mod)
other_mod.extend ClassMethods
end
def instance_method
end
module ClassMethods
def class_method
end
end
end
class Bar
include Foo
end
You can't accomplish this easily as you describe without somehow splitting the included module into multiple pieces, though, unfortunately.
You can, but not quite like that. This is a common pattern for including both instance and class methods in one module.
module Foo
def self.included(base)
base.extend ClassMethods
end
def instance_method
puts 'instance'
end
module ClassMethods
def class_method
puts 'class'
end
end
end
class Bar
include Foo
end
bar = Bar.new
Bar.class_method #=> 'class'
bar.instance_method #=> 'instance'
You are close. You probably noticed that the instance method works fine. The problem with the class method is that self => Foo when it's defined, so it does not respond to Bar. If you add the line puts "I'm a module method" in self.class_method, you will find
Foo.class_method => "I'm a module method"
Here's an easy way to accomplish what you want to do:
module Foo_class
attr_accessor :cat
def class_method
puts "I'm a class method"
end
end
module Foo_instance
def instance_method
puts "I'm an instance method"
end
end
class Bar
extend Foo_class
include Foo_instance
end
Bar.class_method #=> I'm a class method
Bar.cat = "meow"
Bar.cat #=> "meow"
Bar.new.instance_method #=> I'm an instance method
I added a class instance variable, #cat, and an accessor for it, just to show how easy that is to do.
Object#extend is great, because you can just add instance variables and methods to a module, just as you would do with Object#include to mixin instance variables and methods, and extend mixes them in as class instance variables and class methods. You can also do this:
bar = Bar.new
bar.extend Foo_class
to have the instance variables and methods in Foo_class apply to the instance bar.
possibly I'm not explaining the concept very well, but I'm looking to add class methods to a series of ruby classes to enable them to hold class specific information which will then be called by individual instance methods of the classes.
I can make it work, but it is a bit ugly. Can anyone as it requires 2 modules, one included and the other extended (see example code below).
Can anyone think of a more elegant way of implementing this functionality ?
Thanks
Steve
This module is extended to give class methods but adding an instance member to each class it is included in
module My1
def my_methods (*sym_array)
#my_methods=sym_array
end
def method_list
#my_methods
end
end
This module is included to give instance methods
module My2
def foo
self.class.method_list.each { |m| self.send m }
end
end
Now use the modules - the ugliness is having to use an include and extend statement to allow me to pass a set of symbols to a class method which will then be implemented in an
instance
class Foo
extend My1
include My2
my_methods :baz
def baz
puts "Baz!"
end
end
class Bar
extend My1
include My2
my_methods :frodo
def frodo
puts "Frodo!"
end
end
class Wibble < Bar
extend My1
include My2
my_methods :wobble
def wobble
puts "Wobble!"
end
end
Here is the required output - note that each class has its own instance #my_methods so the behaviour is different for the derived class Wibble < Bar
f=Foo.new
b=Bar.new
w=Wibble.new
f.foo #=> "Bar!"
b.foo #=> "Frodo!"
w.foo #=> "Wobble!"
When a module is included, a hook is called on it. You can use that to do the extend you want.
module M1
def self.included(base)
base.extend(M2)
end
end
People often call that second module M1::ClassMethods. If you're using rails, ActiveSupport::Concern encapsulates this pattern
I would suggest to use a hook from module instead:
module MyModule
def self.included(klass)
klass.extend ClassMethods
end
def foo
self.class.method_list.each{ |m| self.send m }
end
module ClassMethods
attr_reader :method_list
def my_methods(*sym_array)
#method_list = sym_array
end
end
end
So it simplifies to call include only a module whenever you want the functionality to given classes.
class Foo
include MyModule
my_methods :baz
def baz
puts "Baz!"
end
end
Say there are three classes: A, B & C. I want each class to have a class method, say self.foo, that has exactly the same code for A, B & C.
Is it possible to define self.foo in a module and include this module in A, B & C? I tried to do so and got an error message saying that foo is not recognized.
Yep
module Foo
def self.included(base)
base.extend(ClassMethods)
end
module ClassMethods
def some_method
# stuff
end
end
end
One possible note I should add - if the module is going to be ALL class methods - better off just using extend ModuleName in the Model and defining the methods directly in the module instead - rather than having a ClassMethods module inside the Module, a la
module ModuleName
def foo
# stuff
end
end
module Common
def foo
puts 'foo'
end
end
class A
extend Common
end
class B
extend Common
end
class C
extend Common
end
A.foo
Or, you can extend the classes afterwards:
class A
end
class B
end
class C
end
[A, B, C].each do |klass|
klass.extend Common
end
Rails 3 introduced a module named ActiveSupport::Concern which has the goal of simplifying the syntax of modules.
module Foo
extend ActiveSupport::Concern
module ClassMethods
def some_method
# stuff
end
end
end
It allowed us to save a few lines of "boilerplate" code in the module.
This is basic ruby mixin functionality that makes ruby so special.
While extend turns module methods into class methods, include turns module methods into instance methods in the including/extending class or module.
module SomeClassMethods
def a_class_method
'I´m a class method'
end
end
module SomeInstanceMethods
def an_instance_method
'I´m an instance method!'
end
end
class SomeClass
include SomeInstanceMethods
extend SomeClassMethods
end
instance = SomeClass.new
instance.an_instance_method => 'I´m an instance method!'
SomeClass.a_class_method => 'I´m a class method'
Just wanted to extend Oliver's answer
Define Class methods and instance methods together in a module.
module Foo
def self.included(base)
base.extend(ClassMethods)
end
module ClassMethods
def a_class_method
puts "ClassMethod Inside Module"
end
end
def not_a_class_method
puts "Instance method of foo module"
end
end
class FooBar
include Foo
end
FooBar.a_class_method
FooBar.methods.include?(:a_class_method)
FooBar.methods.include?(:not_a_class_method)
fb = FooBar.new
fb.not_a_class_method
fb.methods.include?(:not_a_class_method)
fb.methods.include?(:a_class_method)