Custom Hook/Callback/Macro Methods - ruby

How do I create a Custom Hook Method in a Subclass?
No need to duplicate Rails, of course -- the simpler, the better.
My goal is to convert:
class SubClass
def do_this_method
first_validate_something
end
def do_that_method
first_validate_something
end
private
def first_validate_something; end
end
To:
class ActiveClass; end
class SubClass < ActiveClass
before_operations :first_validate_something, :do_this_method, :do_that_method
def do_this_method; end
def do_that_method; end
private
def first_validate_something; end
end
Example in Module: https://github.com/PragTob/after_do/blob/master/lib/after_do.rb
Rails #before_action: http://apidock.com/rails/v4.0.2/AbstractController/Callbacks/ClassMethods/before_action

Here's a solution that uses prepend. When you call before_operations for the first time it creates a new (empty) module and prepends it to your class. This means that when you call method foo on your class, it will look first for that method in the module.
The before_operations method then defines simple methods in this module that first invoke your 'before' method, and then use super to invoke the real implementation in your class.
class ActiveClass
def self.before_operations(before_method,*methods)
prepend( #active_wrapper=Module.new ) unless #active_wrapper
methods.each do |method_name|
#active_wrapper.send(:define_method,method_name) do |*args,&block|
send before_method
super(*args,&block)
end
end
end
end
class SubClass < ActiveClass
before_operations :first_validate_something, :do_this_method, :do_that_method
def do_this_method(*args,&block)
p doing:'this', with:args, and:block
end
def do_that_method; end
private
def first_validate_something
p :validating
end
end
SubClass.new.do_this_method(3,4){ |x| p x }
#=> :validating
#=> {:doing=>"this", :with=>[3, 4], :and=>#<Proc:0x007fdb1301fa18#/tmp.rb:31>}
If you want to make the idea by #SteveTurczyn work you must:
receive the args params in the block of define_method, not as arguments to it.
call before_operations AFTER your methods have been defined if you want to be able to alias them.
class ActiveClass
def self.before_operations(before_method, *methods)
methods.each do |meth|
raise "No method `#{meth}` defined in #{self}" unless method_defined?(meth)
orig_method = "_original_#{meth}"
alias_method orig_method, meth
define_method(meth) do |*args,&block|
send before_method
send orig_method, *args, &block
end
end
end
end
class SubClass < ActiveClass
def do_this_method(*args,&block)
p doing:'this', with:args, and:block
end
def do_that_method; end
before_operations :first_validate_something, :do_this_method, :do_that_method
private
def first_validate_something
p :validating
end
end
SubClass.new.do_this_method(3,4){ |x| p x }
#=> :validating
#=> {:doing=>"this", :with=>[3, 4], :and=>#<Proc:0x007fdb1301fa18#/tmp.rb:31>}

You can alias the original method to a different name (so :do_this_something becomes :original_do_this_something) and then define a new :do_this_something method that calls :first_validate_something and then the original version of the method Something like this...
class ActiveClass
def self.before_operations(before_method, *methods)
methods.each do |method|
alias_method "original_#{method.to_s}".to_sym, method
define_method(method, *args, &block) do
send before_method
send "original_#{method.to_s}", *args, &block
end
end
end
end

This is a way of writing the code that does not make use of aliases. It includes a class method validate that specifies the validator method and the methods that are to call the validator method. This method validate can be invoked multiple times to change the validator and validatees dynamically.
class ActiveClass
end
Place all the methods other than the validators in a subclass of ActiveClass named (say) MidClass.
class MidClass < ActiveClass
def do_this_method(v,a,b)
puts "this: v=#{v}, a=#{a}, b=#{b}"
end
def do_that_method(v,a,b)
puts "that: v=#{v}, a=#{a}, b=#{b}"
end
def yet_another_method(v,a,b)
puts "yet_another: v=#{v}, a=#{a}, b=#{b}"
end
end
MidClass.instance_methods(false)
#=> [:do_this_method, :do_that_method, :yet_another_method]
Place the validators, together with a class method validate, in a subclass of MidClass named (say) SubClass.
class SubClass < MidClass
def self.validate(validator, *validatees)
superclass.instance_methods(false).each do |m|
if validatees.include?(m)
define_method(m) do |v, *args|
send(validator, v)
super(v, *args)
end
else
define_method(m) do |v, *args|
super(v, *args)
end
end
end
end
private
def validator1(v)
puts "valid1, v=#{v}"
end
def validator2(v)
puts "valid2, v=#{v}"
end
end
SubClass.methods(false)
#=> [:validate]
SubClass.private_instance_methods(false)
#=> [:validator1, :validator2]
The class method validate passes symbols for the validation method to use and the methods to be validated. Let's try it.
sc = SubClass.new
SubClass.validate(:validator1, :do_this_method, :do_that_method)
sc.do_this_method(1,2,3)
# valid1, v=1
# this: v=1, a=2, b=3
sc.do_that_method(1,2,3)
# valid1, v=1
# that: v=1, a=2, b=3
sc.yet_another_method(1,2,3)
# yet_another: v=1, a=2, b=3
Now change the validation.
SubClass.validate(:validator2, :do_that_method, :yet_another_method)
sc.do_this_method(1,2,3)
# this: v=1, a=2, b=3
sc.do_that_method(1,2,3)
# valid2, v=1
# that: v=1, a=2, b=3
sc.yet_another_method(1,2,3)
# valid2, v=1
# yet_another: v=1, a=2, b=3
When super is called without arguments from a normal method, all arguments and a block, if there is one, are passed to super. If the method was created with define_method, however, no arguments (and no block) are passed to super. In the latter case the arguments must be explicit.
I wanted to pass a block or proc on to super if there is one, but have been using the wrong secret sauce. I would welcome advice for doing that.

Related

Ruby 2.6: How can I dynamically override instance methods when prepending a module?

I have a module called Notifier.
module Notifier
def self.prepended(host_class)
host_class.extend(ClassMethods)
end
module ClassMethods
def emit_after(*methods)
methods.each do |method|
define_method(method) do |thing, block|
r = super(thing)
block.call
r
end
end
end
end
end
It exposes a class method emit_after. I use it like so:
class Player
prepend Notifier
attr_reader :inventory
emit_after :take
def take(thing)
# ...
end
end
The intention is that by calling emit_after :take, the module overrides #take with its own method.
But the instance method isn't being overridden.
I can however, override it explicitly without using ClassMethods
module Notifier
def self.prepended(host_class)
define_method(:take) do |thing, block|
r = super(thing)
block.call
r
end
end
class Player
prepend Notifier
attr_reader :inventory
def take(thing)
# ...
end
end
#> #player.take #apple, -> { puts "Taking apple" }
#Taking apple
#=> #<Inventory:0x00007fe35f608a98...
I know that ClassMethods#emit_after is called so I assume that the method is being defined but it just never gets called.
I want to create the methods dynamically. How can I ensure that the generate method overrides my instance method?
#Konstantin Strukov's solution is good but maybe a little confusing. So, I suggest another solution, which is more like the original one.
Your first goal is to add a class method (emit_after) to your class. To do that you should use extend method without any hooks such as self.prepended(), self.included() or self.extended().
prepend, as well as include, are used to add or override instance methods. But that is your second goal and it happens when you call emit_after. So you shouldn't use prepend or include when extending your class.
module Notifier
def emit_after(*methods)
prepend(Module.new do
methods.each do |method|
define_method(method) do |thing, &block|
super(thing)
block.call if block
end
end
end)
end
end
class Player
extend Notifier
emit_after :take
def take(thing)
puts thing
end
end
Player.new.take("foo") { puts "bar" }
# foo
# bar
# => nil
Now it is obvious that you call extend Notifier in order to add the emit_after class method and all the magic is hidden in the method.
What about this solution:
module Notifier
def self.[](*methods)
Module.new do
methods.each do |method|
define_method(method) do |thing, &block|
super(thing)
block.call if block
end
end
end
end
end
class Player
prepend Notifier[:take]
def take(thing)
puts "I'm explicitly defined"
end
end
Player.new.take(:foo) { puts "I'm magically prepended" }
# => I'm explicitly defined
# => I'm magically prepended
It's quite similar to the solution from Aleksei Matiushkin, but the ancestors' chain is a bit cleaner (no "useless" Notifier there)
Prepend to the currently opened class:
module Notifier
def self.prepended(host_class)
host_class.extend(ClassMethods)
end
module ClassMethods
def emit_after(*methods)
# ⇓⇓⇓⇓⇓⇓⇓ HERE
prepend(Module.new do
methods.each do |method|
define_method(method) do |thing, block = nil|
super(thing).tap { block.() if block }
end
end
end)
end
end
end
class Player
prepend Notifier
attr_reader :inventory
emit_after :take
def take(thing)
puts "foo"
end
end
Player.new.take :foo, -> { puts "Taking apple" }
#⇒ foo
# Taking apple

How to define an original name scope in module/class with Ruby

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.

Execute method like before_filter in Rails

I try to write a metaprogramming for execute a method before 'master' method. Why ? Because, I have several class and it's ugly to repeat the call in the head of the method
Case :
class MyClass
include MySuperModule
before :method, call: before_method
def before_method
puts "Before.."
end
end
class SomeClass < MyClass
def method
puts "Method.."
end
end
module MySuperModule
# the awesome code
end
Output :
SomeClass.new.method => "Before.. Method.."
So, I try write a module with ClassMethodsor method_missingwithout success.
You don't need a gem for simple metaprogramming like this. What you can do is redefine the "after" method to call the "before" method and then the original "after" method.
This works even when using before multiple times on the same method or when creating a chain of before calls.
module MySuperModule
def before meth, opts
old_method = instance_method(meth)
define_method(meth) do
send opts[:call]
old_method.bind(self).call
end
end
end
class MyClass
extend MySuperModule
def foo
puts "foo"
end
def bar
puts "bar"
end
def baz
puts "baz"
end
before :foo, call: :bar
before :bar, call: :baz
end
MyClass.new.foo
# baz
# bar
# foo
If it is just for subclassing purposes you can take advantage of Module#prepend:
class Superclass
def self.inherited(subclass)
# subclass.send :prepend, Module.new { on Ruby < 2.1
subclass.prepend Module.new {
def method
before_method
super
end
}
end
def before_method
puts 'Before'
end
end
class Subclass < Superclass
def method
puts 'Method'
end
end
Subclass.new.method
#=> Before
#=> Method
What you are looking for is Aspect oriented programming support for ruby. There are several gems implementing this, like aquarium.
Another way to do this is to use the rcapture gem.
It is pretty awesome.
Eg:
require 'rcapture'
class A
# Makes the class intercept able
include RCapture::Interceptable
def first
puts 'first'
end
def second
puts 'second'
end
end
# injects methods to be called before each specified instance method.
A.capture_pre :methods => [:first, :second] do
puts "hello"
end
n = A.new
n.first
n.second
produces:
hello
first
hello
second
Maybe you can use a decorator. In ruby there is a nice gem called 'drapeer'. See Drapper Link
Every call in ruby runs through set_trace_func so you can hook into that and call exactly what you want. Not the prettiest solution and there are better ways but it does work. Another option is the Hooks gem, though I haven't tried it myself, it looks like it should give you the ability to do what you want.
module MySuperModule
# the awesome code
end
class MyClass
include MySuperModule
def before_method
puts "Before.."
end
end
class SomeClass < MyClass
def method
puts "Method.."
end
end
set_trace_func proc { |event, file, line, id, binding, class_name|
if event == "call" && class_name == SomeClass && id == :method
caller = binding.eval("self")
caller.send(:before_method)
end
}
SomeClass.new.method
#=> Before..
#=> Method..

Ruby - Executing same code after most methods in a class

I'm trying to create some kind of module or superclass that wraps one method call after each method of the subclass.
There are some constraints though: I wouldn't want the method to be run after initialize() is called nor after a few other methods of my choice is called.
Another constraint is that I would only want that method to be executed IF the flag #check_ec is set to true.
I have classes with more than 60 methods that I have hard-coded the same piece of code that ispasted all over the place.
Is there a way that I could make a wrapper that would automatically execute that method for my class methods?
So the idea is this:
class Abstract
def initialize(check_ec)
#check_ec = check_ec
end
def after(result) # this is the method that I'd like to be added to most methods
puts "ERROR CODE: #{result[EC]}"
end
def methods(method) # below each method it would execute after
result = method() # execute the given method normally
after(result) if #check_ec and method != :initialize and method != :has_valid_params
end
end
class MyClass < Abstract
def initialize(name, some_stuff, check_error_code)
# do some stuff...
#name = name
super(check_error_code)
end
def my_method_a() # execute after() after this method
return {EC: 0}
end
def my_method_b() # execute after() after this method
return {EC: 7}
end
def has_valid_params() # don't execute after() on this method
return true
end
end
This is trivially easy using method_missing, and composition instead of inheritance. You can build a very simple class which forwards method invocations, and then executes an after callback, except for specific method names:
class Abstract
def initialize(object)
#object = object
end
def method_missing(method, *arguments)
result = #object.send(method, *arguments)
after() unless method == "has_valid_params"
result
end
def after
# whatever
end
end
o = Abstract.new(MyClass.new)
A solution using singleton class.
class MyClass
def initialize(name, some_stuff)
# do some stuff...
#name = name
end
def my_method_a # execute after() after this method
return {EC: 0}
end
def my_method_b() # execute after() after this method
return {EC: 7}
end
def has_valid_params() # don't execute after() on this method
return true
end
end
module ErrorCodeChecker
def after(result) # this is the method that I'd like to be added to most methods
puts "ERROR CODE: #{result[:EC]}"
end
def addErrorCodeCheck(exclude = [])
methods = self.class.superclass.public_instance_methods(false) - exclude
class << self
self
end.class_exec {
methods.each {|method|
define_method(method) {|*p|
super(*p).tap {|res| after(res)}
}
}
}
end
end
class MyClassEC < MyClass
include ErrorCodeChecker
def initialize(name, some_stuff, check_error_code, exclude = [])
super name, some_stuff
addErrorCodeCheck(exclude) if check_error_code
end
end
'addErrorCodeCheck' opens up the singleton class of an instance of MyClassEC, and redefines instance methods of MyClass not in the exclude list. The redefined methods hide the original methods but call them via 'super' method inside before calling 'after'.
You can apply 'addErrorCodeCheck' repeatedly later if needed.
Execution example: (tested in Ruby 1.9.3)
my = MyClassEC.new('test', 'abc', true, [:has_valid_params])
my.my_method_a # => ERROR CODE: 0
my.my_method_b # => ERROR CODE: 7
my.has_valid_params # => (nothing)
What about this? It has a major drawback which is that your methods must be already defined before calling check_error_code, but it may suit your needs. You could look for inspiration for a better solution in Rails callbacks, or defer the redefinition of each method until that method is added using the method_added hook.
Include ErrorCodeChecker and call check_error_code in each class you want to check the error code (as in the last line of the snippet).
module ErrorCodeChecker
def self.included(base)
base.send(:extend, ClassMethods)
end
def after(result) # this is the method that I'd like to be added to most methods
puts "ERROR CODE: #{result[:ec]}"
end
module ClassMethods
def check_error_code(options = {})
check_on = instance_methods(false) - Array(options[:except])
check_on &= Array(options[:only]) if options[:only]
class_eval do
check_on.each do |method|
alias_method "#{ method }_without_ec", method
define_method(method) do |*args, &block|
send("#{ method }_without_ec", *args, &block).tap { |result| after(result) if #check_ec }
#if you want to actually return the return value of calling after:
#result = send("#{ method }_without_ec")
##check_ec ? after(result) : result
end
end
end
end
end
end
class Abstract
include ErrorCodeChecker
def initialize(check_ec)
#check_ec = check_ec
end
end
class MyClass < Abstract
def initialize(name, some_stuff, check_error_code)
# do some stuff...
#name = name
super(check_error_code)
end
def my_method_a # execute after() after this method
{ec: 0}
end
def my_method_b # execute after() after this method
{ec: 7}
end
def has_valid_params # don't execute after() on this method
true
end
check_error_code except: :has_valid_params
#or whitelisting:
#check_error_code only: [:my_method_a, :my_method_b]
#or both:
#check_error_code only: :my_method_a, except: [:has_valid_params, dont_check_this_one]
end

Ruby class_eval method

I'm trying to figure out how to dynamically create methods
class MyClass
def initialize(dynamic_methods)
#arr = Array.new(dynamic_methods)
#arr.each { |m|
self.class.class_eval do
def m(*value)
puts value
end
end
}
end
end
tmp = MyClass.new ['method1', 'method2', 'method3']
Unfortunately this only creates the method m but I need to create methods based on the value of m, ideas?
There are two accepted ways:
Use define_method:
#arr.each do |method|
self.class.class_eval do
define_method method do |*arguments|
puts arguments
end
end
end
Use class_eval with a string argument:
#arr.each do |method|
self.class.class_eval <<-EVAL
def #{method}(*arguments)
puts arguments
end
EVAL
end
The first option converts a closure to a method, the second option evaluates a string (heredoc) and uses regular method binding. The second option has a very slight performance advantage when invoking the methods. The first option is (arguably) a little more readable.
define_method(m) do |*values|
puts value
end

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