Suppose I have a module like this:
module MyAssigments
def dummy_assignment=(value)
puts "it's not assigned #{value}"
end
end
and a class that includes it like this:
class MyClass
include MyAssigments
def x=(value)
dummy_assignment=(value)
end
end
then
o = MyClass.new
o.x="anything"
does not print anything on screen, why ?
Ruby has a syntax/paring quirk here: using an assginemnt method for self has to be explicitly qualified thus:
def x=(value)
self.dummy_assignment=value
end
without the self. part, it is assumed by ruby to be an assignment to a local variable.
Related
How do I pass processor_pool to the method inside the module?
class Dummy
def initialize
processor_pool = Concurrent::FixedThreadPool.new(10)
#threadpool = Module.new do
extend Concurrent::Promises::FactoryMethods
def self.default_executor
return processor_pool # this cannot find the processor_pool variable
end
end
end
end
I get the same error even if I make it an instance variable like #processor_pool
Something like this (I simplified your class a bit to get rid of dependencies for the sake of example, but its structure is the same):
class Dummy
attr_reader :threadpool
def initialize
processor_pool = "It works"
#threadpool = Module.new do
define_method :default_executor do
return processor_pool
end
module_function :default_executor
end
end
end
Dummy.new.threadpool.default_executor # => "It works"
How to define an original name scope in module/class with Ruby
I want to implement class like the following:
module SomeModule
extend OriginalNameScope
scope(:some) do
def method1
puts 1
end
def method2
puts 2
end
end
end
class SomeClass
include SomeModule
end
c = SomeClass.new
# I want to call methods like the following:
c.some_method1
c.some_method2
How to implement the OriginalNameScope module? I found out to get the method definitions in this method, but I don't know how to redefine methods with a prefix scope.
module OriginalNameScope
def scope(name, &method_definition)
puts method_definition.class
# => Proc
end
end
This is actually just a combination of some simple standard Ruby metaprogramming patterns and idioms:
module OriginalNameScope
def scope(name)
singleton_class.prepend(Module.new do
define_method(:method_added) do |meth|
if name && !#__recursion_guard__
#__recursion_guard__ = meth
method = instance_method(meth)
undef_method(meth)
define_method(:"#{name}_#{meth}") do |*args, &block|
method.bind(self).(*args, &block)
end
end
#__recursion_guard__ = nil
super(meth)
end
end)
yield
end
end
I just slapped this together, there's probably a lot that can be improved (e.g. use Refinements) and simplified.
I know I can execute the following to add methods to the String class
class String
def do_something
puts self.size
end
end
var = "test"
var.do_something
and this will return 4
I want to be able to have a module with a function that takes in a String, but be able to call the do_something method on this string (see below for example) - is it possible?
EDIT: Added sample code that is not working
module TestModule
class String
def do_something
puts self.size
end
end
def self.test(str)
str.do_something
end
end
This gives the error: undefined method 'do_something' for "hello":String (NoMethodError)
The way your code is written, you're defining a new class called TestModule::String. If you want to modify the built-in Ruby String class, you need to use the fully-qualified name of String (with the ""::") if you want to keep the declaration inside the module.
module TestModule
class ::String
def do_something
puts self.size
end
end
def self.test(str)
str.do_something
end
end
Adding the "::" tells Ruby that the String class that you want is not part of the TestModule.
It's probably cleaner to just declare String outside of TestModule in the same file.
If you don't want to pollute the global String class, you could just modify the specific String instance that you want to add the method to.
module TestModule
def self.test(str)
do_somethingify!(str)
str.do_something
end
def self.do_somethingify!(str)
unless str.respond_to? :do_something
str.instance_eval do
def do_something
puts size
end
end
end
end
end
Maybe this?
module TestModule
module_function
def test(str)
str.instance_eval{doSomething}
end
end
Test.test(str)
Edit Changed due to the change in the question
Just put the definition of doSomething outside out the TestModule class.
class String
def doSomething
puts size
end
end
module TestModule
module_function
def test(str)
str.doSomething
end
end
class Foo
include Module.new { class_eval "def lab; puts 'm' end" }
def lab
super
puts 'c'
end
end
Foo.new.lab #=> m c
========================================================================
class Foo
include Module.new { instance_eval "def lab; puts 'm' end" }
def lab
super
puts 'c'
end
end
Notice here I changed class_eval to instance_eval
Foo.new.lab rescue nil#=> no super class method lab
Foo.lab #=> undefined method lab for Foo class
So it seems that including the module neither defined an instance method nor a class method.
Any explanation what's going on here?
This code was tested on ruby 1.8.7 on mac.
First, think of what include does. it makes the instance methods of the module being included into instance methods on the including class. i.e. apart from the fact that your working example uses an anonymous module it is equivalent to:
module M1
def lab
puts 'm'
end
end
class Foo
include M1
def lab
super
puts 'c'
end
end
Next, think of what class_eval does. It evaluates the given code in the context of the class or module. i.e. it's exactly like you reopened the module and typed the code passed to class_eval. So MyModule = Module.new { class_eval "def lab; puts 'm' end" } is equivalent to
module MyModule
def lab
puts 'm'
end
end
Hopefully this explains the case that works.
When you use instance_eval you are evaluating the code within the context of the receiving object (in this case the instance of module) so MyMod2 = Module.new { instance_eval "def lab; puts 'm' end" } is equivalent to
module MyMod2
def MyMod2.lab
puts 'm'
end
end
i.e. it creates a module method which you'd call via MyMod2.lab and such methods are not added as instance methods by include.
Please note: this answer borrows a bit of its explanation from an answer I wrote to a previous question asking about instance_eval vs. class_eval relating to an example from The Ruby Programming Language book. You might find that answer helpful too.
including a module just takes the instance methods - you are looking for extend. luckily to get the best of both worlds, you can simply do:
module Something
def self.included(base)
base.extend ClassMethods
end
module ClassMethods
def blah
puts "lol"
end
end
end
class Test
include Something
end
irb:
>> Test.blah
lol
=> nil
I need to define the constant in the module that use the method from the class that includes this module:
module B
def self.included(base)
class << base
CONST = self.find
end
end
end
class A
def self.find
"AAA"
end
include B
end
puts A::CONST
But the compiler gives the error on the 4th line.
Is there any other way to define the constant?
The more idiomatic way to achieve this in Ruby is:
module B
def self.included(klass)
klass.class_eval <<-ruby_eval
CONST = find
ruby_eval
# note that the block form of class_eval won't work
# because you can't assign a constant inside a method
end
end
class A
def self.find
"AAA"
end
include B
end
puts A::CONST
What you were doing (class << base) actually puts you into the context of A's metaclass, not A itself. The find method is on A itself, not its metaclass. The thing to keep in mind is that classes are themselves objects, and so have their own metaclasses.
To try to make it clearer:
class Human
def parent
# this method is on the Human class and available
# to all instances of Human.
end
class << self
def build
# this method is on the Human metaclass, and
# available to its instance, Human itself.
end
# the "self" here is Human's metaclass, so build
# cannot be called.
end
def self.build
# exactly the same as the above
end
build # the "self" here is Human itself, so build can
# be called
end
Not sure if that helps, but if you don't understand it, you can still use the class_eval idiom above.
In your specific case.
module B
def self.included(base)
base.const_set("CONST", base.find)
end
end
class A
def self.find
"AAA"
end
include B
end
puts A::CONST
Despite it works, it's a little bit messy. Are you sure you can't follow a different way to achieve your goal?
module B
def self.included(base)
class << base
CONST = self.find
end
end
end
class A
class << self
def self.find
"AAA"
end
end
include B
end
then the compiler error is fixed, pls try.