class_name = "TestClass"
Object.const_set class_name,Class.new{
include MOduleX
}
#module_x.rb
module ModuleX
def ModuleX.included (klass)
p klass.name #=> nil
end
end
I need to access the name of the class ("TestClass" in this case) inside the module, how can I do it?
You can't, const_set is occuring after Class.new. At the point where ModuleX is included (MOduleX is, I assume, a typo), the class is well and truly nameless.
Not to even mention that a constant can't be called test, as Ruby grammar mandates that constants must start with a capital letter.
However, if your module must know the class name at inclusion time, it's probably doing something wrong. I suggest rethinking and refactoring.
#Amadan has explained why that won't work, but you can get it if you are able to write it like this:
class_name = "Test"
module ModuleX
def self.included(klass)
puts "klass = #{klass}"
end
end
Object.const_set class_name, Class.new do
end.include ModuleX
#=> "klass = Test"
I am still trying to clearly understand Module/Class/Instance variables ...
My code currently looks something like this ...
module Foo
##var1 ={}
##var2 =[]
##var3 = nil
def m1(value)
##var2 << value
end
def m2(value)
##var1[##var3]=value
end
end
class Bar
include Foo
p ##var1
end
class Bar2
include Foo
p #var1
end
I am trying to create a module that contains a class-wide configuration for how each class will behave. The configuration is stored in ##var1 and ##var2. Using this code the variables are shared across ALL classes that include the module. This is not the desire result, I want each class to have it's own behavior configuration.
I have also tried creating a single class that includes the module and also creates the variables but then the variables are not accessible by the module.
module Foo
def m1(value)
##var2 << value
end
def m2(value)
##var1[##var3]=value
end
end
class T
##var1 ={}
##var2 =[]
##var3 = nil
include foo
end
class Bar < T
p ##var1
end
class Bar2 < T
p #var1
end
I have also read that having modules with class variables is not good coding style but I cannot think of a way to achieve my functionality with this ...
Thanks in advance for any help
Firstly - class variables are evil and should be avoided (because they are also inherited by all subclasses and usually causes more harm than good.
You want to create a class instance variable (not class variable) on a class or module which is including given module. It is easy to do with included method:
module Foo
#default_settings = {}
module ClassMethods
def foo_settings
#foo_settings
end
end
def self.included(target)
target.instance_variable_set('#foo_settings', #default_settings.dup)
target.extend ClassMethods
end
end
(ruby noob here..apologies if I'm not asking the question correctly)
So I have two files, one contains a module which holds a class....
file_alpha.rb :
class alpha
def a_name
do stuff
end
end
file_beta.rb:
module STUFF_IN_BETA
class beta
def b_name
do more stuff
end
end
end
So I want to access 'def b_name' inside file_alpha but I'm not sure how...
class alpha
def a_name
do stuff
b_name() <----HOW TO DO this?
end
end
How do I make the method 'b_name' available to class alpha?
If you want b to be a module that adds methods to a, ditch the class inside it, and just do:
class a
include STUFF_IN_BETA
def a
do stuff
b # this will call method b
end
end
module STUFF_IN_BETA
def b
do more stuff
end
end
You need to include your class
require 'b.rb'
And then call the method
b.b()
Something like:
file_beta.rb
module StuffInBeta
def b
do more stuff
end
end
file_alpha.rb
require 'file_beta'
class A
def a
do stuff
b # from the module
end
end
I'm trying to override a dynamically-generated method by including a module.
In the example below, a Ripple association adds a rows= method to Table. I want to call that method, but also do some additional stuff afterwards.
I created a module to override the method, thinking that the module's row= would be able to call super to use the existing method.
class Table
# Ripple association - creates rows= method
many :rows, :class_name => Table::Row
# Hacky first attempt to use the dynamically-created
# method and also do additional stuff - I would actually
# move this code elsewhere if it worked
module RowNormalizer
def rows=(*args)
rows = super
rows.map!(&:normalize_prior_year)
end
end
include RowNormalizer
end
However, my new rows= is never called, as evidenced by the fact that if I raise an exception inside it, nothing happens.
I know the module is getting included, because if I put this in it, my exception gets raised.
included do
raise 'I got included, woo!'
end
Also, if instead of rows=, the module defines somethingelse=, that method is callable.
Why isn't my module method overriding the dynamically-generated one?
Let's do an experiment:
class A; def x; 'hi' end end
module B; def x; super + ' john' end end
A.class_eval { include B }
A.new.x
=> "hi" # oops
Why is that? The answer is simple:
A.ancestors
=> [A, B, Object, Kernel, BasicObject]
B is before A in the ancestors chain (you can think of this as B being inside A). Therefore A.x always takes priority over B.x.
However, this can be worked around:
class A
def x
'hi'
end
end
module B
# Define a method with a different name
def x_after
x_before + ' john'
end
# And set up aliases on the inclusion :)
# We can use `alias new_name old_name`
def self.included(klass)
klass.class_eval {
alias :x_before :x
alias :x :x_after
}
end
end
A.class_eval { include B }
A.new.x #=> "hi john"
With ActiveSupport (and therefore Rails) you have this pattern implemented as alias_method_chain(target, feature) http://apidock.com/rails/Module/alias_method_chain:
module B
def self.included(base)
base.alias_method_chain :x, :feature
end
def x_with_feature
x_without_feature + " John"
end
end
Update Ruby 2 comes with Module#prepend, which does override the methods of A, making this alias hack unnecessary for most use cases.
Why isn't my module method overriding the dynamically-generated one?
Because that's not how inheritance works. Methods defined in a class override the ones inherited from other classes/modules, not the other way around.
In Ruby 2.0, there's Module#prepend, which works just like Module#include, except it inserts the module as a subclass instead of a superclass in the inheritance chain.
If you extend the instance of the class, you will can do it.
class A
def initialize
extend(B)
end
def hi
'hi'
end
end
module B
def hi
super[0,1] + 'ello'
end
end
obj = A.new
obj.hi #=> 'hello'
Background:
I have a module which declares a number of instance methods
module UsefulThings
def get_file; ...
def delete_file; ...
def format_text(x); ...
end
And I want to call some of these methods from within a class. How you normally do this in ruby is like this:
class UsefulWorker
include UsefulThings
def do_work
format_text("abc")
...
end
end
Problem
include UsefulThings brings in all of the methods from UsefulThings. In this case I only want format_text and explicitly do not want get_file and delete_file.
I can see several possible solutions to this:
Somehow invoke the method directly on the module without including it anywhere
I don't know how/if this can be done. (Hence this question)
Somehow include Usefulthings and only bring in some of it's methods
I also don't know how/if this can be done
Create a proxy class, include UsefulThings in that, then delegate format_text to that proxy instance
This would work, but anonymous proxy classes are a hack. Yuck.
Split up the module into 2 or more smaller modules
This would also work, and is probably the best solution I can think of, but I'd prefer to avoid it as I'd end up with a proliferation of dozens and dozens of modules - managing this would be burdensome
Why are there lots of unrelated functions in a single module? It's ApplicationHelper from a rails app, which our team has de-facto decided on as the dumping ground for anything not specific enough to belong anywhere else. Mostly standalone utility methods that get used everywhere. I could break it up into seperate helpers, but there'd be 30 of them, all with 1 method each... this seems unproductive
I think the shortest way to do just throw-away single call (without altering existing modules or creating new ones) would be as follows:
Class.new.extend(UsefulThings).get_file
If a method on a module is turned into a module function you can simply call it off of Mods as if it had been declared as
module Mods
def self.foo
puts "Mods.foo(self)"
end
end
The module_function approach below will avoid breaking any classes which include all of Mods.
module Mods
def foo
puts "Mods.foo"
end
end
class Includer
include Mods
end
Includer.new.foo
Mods.module_eval do
module_function(:foo)
public :foo
end
Includer.new.foo # this would break without public :foo above
class Thing
def bar
Mods.foo
end
end
Thing.new.bar
However, I'm curious why a set of unrelated functions are all contained within the same module in the first place?
Edited to show that includes still work if public :foo is called after module_function :foo
Another way to do it if you "own" the module is to use module_function.
module UsefulThings
def a
puts "aaay"
end
module_function :a
def b
puts "beee"
end
end
def test
UsefulThings.a
UsefulThings.b # Fails! Not a module method
end
test
If you want to call these methods without including module in another class then you need to define them as module methods:
module UsefulThings
def self.get_file; ...
def self.delete_file; ...
def self.format_text(x); ...
end
and then you can call them with
UsefulThings.format_text("xxx")
or
UsefulThings::format_text("xxx")
But anyway I would recommend that you put just related methods in one module or in one class. If you have problem that you want to include just one method from module then it sounds like a bad code smell and it is not good Ruby style to put unrelated methods together.
To invoke a module instance method without including the module (and without creating intermediary objects):
class UsefulWorker
def do_work
UsefulThings.instance_method(:format_text).bind(self).call("abc")
...
end
end
Not sure if someone still needs it after 10 years but I solved it using eigenclass.
module UsefulThings
def useful_thing_1
"thing_1"
end
class << self
include UsefulThings
end
end
class A
include UsefulThings
end
class B
extend UsefulThings
end
UsefulThings.useful_thing_1 # => "thing_1"
A.new.useful_thing_1 # => "thing_1"
B.useful_thing_1 # => "thing_1"
Firstly, I'd recommend breaking the module up into the useful things you need. But you can always create a class extending that for your invocation:
module UsefulThings
def a
puts "aaay"
end
def b
puts "beee"
end
end
def test
ob = Class.new.send(:include, UsefulThings).new
ob.a
end
test
A. In case you, always want to call them in a "qualified", standalone way (UsefulThings.get_file), then just make them static as others pointed out,
module UsefulThings
def self.get_file; ...
def self.delete_file; ...
def self.format_text(x); ...
# Or.. make all of the "static"
class << self
def write_file; ...
def commit_file; ...
end
end
B. If you still want to keep the mixin approach in same cases, as well the one-off standalone invocation, you can have a one-liner module that extends itself with the mixin:
module UsefulThingsMixin
def get_file; ...
def delete_file; ...
def format_text(x); ...
end
module UsefulThings
extend UsefulThingsMixin
end
So both works then:
UsefulThings.get_file() # one off
class MyUser
include UsefulThingsMixin
def f
format_text # all useful things available directly
end
end
IMHO it's cleaner than module_function for every single method - in case want all of them.
As I understand the question, you want to mix some of a module's instance methods into a class.
Let's begin by considering how Module#include works. Suppose we have a module UsefulThings that contains two instance methods:
module UsefulThings
def add1
self + 1
end
def add3
self + 3
end
end
UsefulThings.instance_methods
#=> [:add1, :add3]
and Fixnum includes that module:
class Fixnum
def add2
puts "cat"
end
def add3
puts "dog"
end
include UsefulThings
end
We see that:
Fixnum.instance_methods.select { |m| m.to_s.start_with? "add" }
#=> [:add2, :add3, :add1]
1.add1
2
1.add2
cat
1.add3
dog
Were you expecting UsefulThings#add3 to override Fixnum#add3, so that 1.add3 would return 4? Consider this:
Fixnum.ancestors
#=> [Fixnum, UsefulThings, Integer, Numeric, Comparable,
# Object, Kernel, BasicObject]
When the class includes the module, the module becomes the class' superclass. So, because of how inheritance works, sending add3 to an instance of Fixnum will cause Fixnum#add3 to be invoked, returning dog.
Now let's add a method :add2 to UsefulThings:
module UsefulThings
def add1
self + 1
end
def add2
self + 2
end
def add3
self + 3
end
end
We now wish Fixnum to include only the methods add1 and add3. Is so doing, we expect to get the same results as above.
Suppose, as above, we execute:
class Fixnum
def add2
puts "cat"
end
def add3
puts "dog"
end
include UsefulThings
end
What is the result? The unwanted method :add2 is added to Fixnum, :add1 is added and, for reasons I explained above, :add3 is not added. So all we have to do is undef :add2. We can do that with a simple helper method:
module Helpers
def self.include_some(mod, klass, *args)
klass.send(:include, mod)
(mod.instance_methods - args - klass.instance_methods).each do |m|
klass.send(:undef_method, m)
end
end
end
which we invoke like this:
class Fixnum
def add2
puts "cat"
end
def add3
puts "dog"
end
Helpers.include_some(UsefulThings, self, :add1, :add3)
end
Then:
Fixnum.instance_methods.select { |m| m.to_s.start_with? "add" }
#=> [:add2, :add3, :add1]
1.add1
2
1.add2
cat
1.add3
dog
which is the result we want.
After almost 9 years here's a generic solution:
module CreateModuleFunctions
def self.included(base)
base.instance_methods.each do |method|
base.module_eval do
module_function(method)
public(method)
end
end
end
end
RSpec.describe CreateModuleFunctions do
context "when included into a Module" do
it "makes the Module's methods invokable via the Module" do
module ModuleIncluded
def instance_method_1;end
def instance_method_2;end
include CreateModuleFunctions
end
expect { ModuleIncluded.instance_method_1 }.to_not raise_error
end
end
end
The unfortunate trick you need to apply is to include the module after the methods have been defined. Alternatively you may also include it after the context is defined as ModuleIncluded.send(:include, CreateModuleFunctions).
Or you can use it via the reflection_utils gem.
spec.add_dependency "reflection_utils", ">= 0.3.0"
require 'reflection_utils'
include ReflectionUtils::CreateModuleFunctions
This old question comes to me today when I am studing Ruby and found interesting so I want to answer with my new knowlege.
Assume that you have the module
module MyModule
def say
'I say'
end
def cheer
'I cheer'
end
end
then with the class so call Animal I can take cheer method from MyModule as following
class Animal
define_method(:happy, MyModule.method(:cheer))
end
This is so called unbound method, so you can take a callable object and bind it to another place(s).
From this point, you can use the method as usual, such as
my_dog = Animal.new
my_dog.happy # => "I cheer"
Hope this help as I also learned something new today.
To learn further, you can use irb and take a look at Method object.