Identifying a Ruby module method invoked by super? - ruby

Ruby 2.7+.
I have methods in a couple of modules that are mixed in, and are invoked with super. Each of the module methods invokes super in turn, so all methods by that name in the mixed-in modules are invoked, although perhaps not in a deterministic order.
My question is: Can a method tell programmatically (as opposed to hard-coding) from what module it's been mixed in?
module A
def initialize(*args, **kwargs)
puts("something magic")
end
end
module B
def initialize(*args, **kwargs)
puts("something magic")
end
end
class C
include A
include B
def initialize(*args, **kwargs)
puts("actual #{class.name} initialize")
super
end
end
When run, this will print three lines. What I'm seeking is something like class.name, specific to each module, that identifies the module that supplied the initialize method that's running. The "something magic* strings would be replaced with this actual magic. 🙂
Thanks!

My first attempt was to call super_method to get all the initializers up the stack:
module A
def initialize
A # return for comparison
end
end
module B
def initialize
B
end
end
class C
include A
include B
def initialize
C
end
def super_initializers
init = method(:initialize)
while init
print init.call, " == " # get hardcoded module from `initialize`
p init.owner # get the module dynamically
init = init.super_method # keep getting the super method
end
end
end
>> C.new.super_initializers
C == C
B == B
A == A
== BasicObject
Second idea is to use Module.nesting, I think this is what you're looking for:
module A
def initialize
# i, o, m = method(:initialize), [], Module.nesting[0]
# while i; o << i.owner; i = i.super_method; end
# print "prev "; p o[o.index(m)-1] # previous super
puts "A == #{Module.nesting[0]}"
# print "next "; p o[o.index(m)+1] # next super
super
end
end
module B
def initialize
puts "B == #{Module.nesting[0]}"
super
end
end
# add a class
class Y
def initialize
puts "Y == #{Module.nesting[0]}"
super
end
end
# add some nesting
module X
class Z < Y
def initialize
puts "Z == #{Module.nesting[0]}"
super
end
end
end
class C < X::Z
include A
include B
def initialize
puts "C == #{Module.nesting[0]}"
super
end
end
>> C.new
C == C
B == B
A == A
Z == X::Z
Y == Y
Actually, never thought about that this could be useful, but it works:
def super_trace m
while m;
p m.owner; m = m.super_method
end
end
>> super_trace User.new.method(:save)
ActiveRecord::Suppressor
ActiveRecord::Transactions
ActiveRecord::Validations
ActiveRecord::Persistence
https://rubyapi.org/3.1/o/module#method-c-nesting
https://rubyapi.org/3.1/o/method#method-i-super_method

Related

How to know from what module user was called

I have 2 modules and 1 class:
module B
def hi
say 'hi'
end
end
module C
def say(message)
puts "#{message} from ???"
end
end
class A
include B
include C
end
A.new.hi
#=> hi from ???"
How i can get message as hi from B?
You could use caller_locations to determine the calling method's name, and use that information to retrieve the method's owner:
module C
def say(message)
method_name = caller_locations(1, 1)[0].base_label
method_owner = method(method_name).owner
puts "#{message} from #{method_owner}"
end
end
But this is very brittle. It would be much easier to simply pass the calling module, e.g.:
module B
def hi
say 'hi', B
end
end
module C
def say(message, mod)
puts "#{message} from #{mod}"
end
end
You can use Kenel#__method__ with Method#owner:
module C
def say(message)
puts "#{message} from #{method(__method__).owner }"
end
end
class A
include C
end
A.new.say('hello')
#=> hello from C
Kenel#__method__:
Returns the name at the definition of the current method as a Symbol.
If called outside of a method, it returns nil.
Method#owner:
Returns the class or module that defines the method.

Ruby module prepend vs derivation

What are the differences between:
module Mod
def here
puts 'child'
end
end
class A
prepend Mod
def here
puts 'parent'
end
end
and
class A
def here
puts 'parent'
end
end
class B < A
def here
puts 'child'
end
end
Or another way to put it: is derivating a class the same as prepending a module of the child's code?
No, it is not. B can only inherit from one class, but Mod can be prepended to many classes. If you were to call super inside B#here, it would always refer to A#here, but inside of Mod#here, it will refer to the #here instance method of whatever class Mod was prepended to:
module Mod
def here
super + ' Mod'
end
end
class A
prepend Mod
def here
'A'
end
end
class B
prepend Mod
def here
'B'
end
end
A.new.here
# => 'A Mod'
B.new.here
# => 'B Mod'
and
class A
def here
'A'
end
end
class B
def here
'B'
end
end
class C < A
def here
super + ' C'
end
end
C.new.here
# => 'A C'
class C < B
def here
super + ' C'
end
end
# TypeError: superclass mismatch for class C
No, it's totally different.
One can prepend as many modules as he wants.
module A
def foo; "A" end
end
module B
def foo; "B" end
end
class C
prepend A, B # Prepending is done by this line
def foo; "C" end
end
### take a look at it!
C.ancestors # => [A, B, C, Object, Kernel, BasicObject]
C.new.foo # => "A"
Ruby implements prepend and inheritance using different ways.
prepend is internally achieved by including modules, which causes the surprising ancestors.
here is another question about prepend which may be helpful.

Ruby: storing a value at inclusion time

In a Ruby class, I'd like to store the value of a variable at the time it includes a given module. Below is a contrived example:
module M
def self.included(base)
base.class_eval do
##inclusion_time = Time.now
def included_at
##inclusion_time
end
end
end
end
class A
include M
end
sleep 3
class B
include M
end
sleep 3
class C
include M
end
a = A.new
b = B.new
c = C.new
puts a.included_at
puts b.included_at
puts c.included_at
I've tried this any number of ways (attr_accessor, set_constant, etc,) but the end result is always the same. All of the classes have whatever value was set last.
How do I work around this?
module M
def self.included _
#inclusion_time = Time.now
end
def included_at
self.class.instance_eval{#inclusion_time}
end
end

how to get (and set) variables inside a ruby class?

I update this question to better reflect what I have problems to grasp. The example below kind of work but how can I access the Sub class then I have defined it inside the Base class? Should it not be better to do the call outside the class? If so how do I do that? The second question I have in this example is how to grab values so I can use them in another class. Here I store the values in an array that I later need to unpack in another class. Should I not be able to use a proc for this?
Basically what I want to do is to sort the methods into two different classes depending on if they are nested or not.
class Sub
def initialize(base_class_method)
#base_class_method = base_class_method
#sub_methods = []
end
# omitted code here
def base_class_method
#base_class_method
end
def sub_actions(method)
#sub_methods << method
end
def return_sub_methods
#sub_methods
end
def method_missing(sub_method, &block)
if sub_method
sub_method
else
super
end
end
end
class Base
def initialize
#base_methods = []
end
# omitted code here
def base_actions(method)
#base_methods << method
end
def return_base_methods
#base_methods
end
def method_missing(method, &block)
if block_given?
Sub.new(method).instance_eval(&block)
elsif method
base_actions(method)
else
super
end
end
end
base = Base.new
base.instance_eval do
something1
something_with_a_block do
something_inside_block1_1
something_inside_block1_2
end
something2
something_with_a_block2_2 do
something_inside_block2_1
end
end
p base.return_base_methods #=> [:something1, :something2] works!
You can do something like this.
class Test
# reserved method to instantiate object
def initialize(a,b,c)
#a = a
#b = b
#c = c
end
# getters
def a
#a
end
def b
#b
end
def c
#c
end
def abc
[#a, #b, #c] # returns an array
end
# setters
def a=(var)
#a = var
end
def b=(var)
#b = var
end
def c=(var)
#c = var
end
# set values all at once
def update(a, b, c)
#a = a
#b = b
#c = c
end
end
z = Test.new('something','something','something')
z.update('something!','nothing!',"a thing!")
z.a
z.b
z.c
z.a = 'wow, new value!'

How to implement a "callback" in Ruby?

I'm not sure of the best idiom for C style call-backs in Ruby - or if there is something even better ( and less like C ). In C, I'd do something like:
void DoStuff( int parameter, CallbackPtr callback )
{
// Do stuff
...
// Notify we're done
callback( status_code )
}
Whats a good Ruby equivalent? Essentially I want to call a passed in class method, when a certain condition is met within "DoStuff"
The ruby equivalent, which isn't idiomatic, would be:
def my_callback(a, b, c, status_code)
puts "did stuff with #{a}, #{b}, #{c} and got #{status_code}"
end
def do_stuff(a, b, c, callback)
sum = a + b + c
callback.call(a, b, c, sum)
end
def main
a = 1
b = 2
c = 3
do_stuff(a, b, c, method(:my_callback))
end
The idiomatic approach would be to pass a block instead of a reference to a method. One advantage a block has over a freestanding method is context - a block is a closure, so it can refer to variables from the scope in which it was declared. This cuts down on the number of parameters do_stuff needs to pass to the callback. For instance:
def do_stuff(a, b, c, &block)
sum = a + b + c
yield sum
end
def main
a = 1
b = 2
c = 3
do_stuff(a, b, c) { |status_code|
puts "did stuff with #{a}, #{b}, #{c} and got #{status_code}"
}
end
This "idiomatic block" is a very core part of everyday Ruby and is covered frequently in books and tutorials. The Ruby information section provides links to useful [online] learning resources.
The idiomatic way is to use a block:
def x(z)
yield z # perhaps used in conjunction with #block_given?
end
x(3) {|y| y*y} # => 9
Or perhaps converted to a Proc; here I show that the "block", converted to a Proc implicitly with &block, is just another "callable" value:
def x(z, &block)
callback = block
callback.call(z)
end
# look familiar?
x(4) {|y| y * y} # => 16
(Only use the above form to save the block-now-Proc for later use or in other special cases as it adds overhead and syntax noise.)
However, a lambda can be use just as easily (but this is not idiomatic):
def x(z,fn)
fn.call(z)
end
# just use a lambda (closure)
x(5, lambda {|y| y * y}) # => 25
While the above approaches can all wrap "calling a method" as they create closures, bound Methods can also be treated as first-class callable objects:
class A
def b(z)
z*z
end
end
callable = A.new.method(:b)
callable.call(6) # => 36
# and since it's just a value...
def x(z,fn)
fn.call(z)
end
x(7, callable) # => 49
In addition, sometimes it's useful to use the #send method (in particular if a method is known by name). Here it saves an intermediate Method object that was created in the last example; Ruby is a message-passing system:
# Using A from previous
def x(z, a):
a.__send__(:b, z)
end
x(8, A.new) # => 64
Happy coding!
Explored the topic a bit more and updated the code.
The following version is an attempt to generalize the technique, although remaining extremely simplified and incomplete.
I largely stole - hem, found inspiration in - the implementation of callbacks of DataMapper, which seems to me quite complete and beatiful.
I strongly suggest to have a look at the code # http://github.com/datamapper/dm-core/blob/master/lib/dm-core/support/hook.rb
Anyway, trying to reproduce the functionality using the Observable module was quite engaging and instructive.
A few notes:
method added seems to be require because the original instance methods are not available at the moment of registering the callbacks
the including class is made both observed and self-observer
the example is limited to the instance methods, does not support blocks, args and so on
code:
require 'observer'
module SuperSimpleCallbacks
include Observable
def self.included(klass)
klass.extend ClassMethods
klass.initialize_included_features
end
# the observed is made also observer
def initialize
add_observer(self)
end
# TODO: dry
def update(method_name, callback_type) # hook for the observer
case callback_type
when :before then self.class.callbacks[:before][method_name.to_sym].each{|callback| send callback}
when :after then self.class.callbacks[:after][method_name.to_sym].each{|callback| send callback}
end
end
module ClassMethods
def initialize_included_features
#callbacks = Hash.new
#callbacks[:before] = Hash.new{|h,k| h[k] = []}
#callbacks[:after] = #callbacks[:before].clone
class << self
attr_accessor :callbacks
end
end
def method_added(method)
redefine_method(method) if is_a_callback?(method)
end
def is_a_callback?(method)
registered_methods.include?(method)
end
def registered_methods
callbacks.values.map(&:keys).flatten.uniq
end
def store_callbacks(type, method_name, *callback_methods)
callbacks[type.to_sym][method_name.to_sym] += callback_methods.flatten.map(&:to_sym)
end
def before(original_method, *callbacks)
store_callbacks(:before, original_method, *callbacks)
end
def after(original_method, *callbacks)
store_callbacks(:after, original_method, *callbacks)
end
def objectify_and_remove_method(method)
if method_defined?(method.to_sym)
original = instance_method(method.to_sym)
remove_method(method.to_sym)
original
else
nil
end
end
def redefine_method(original_method)
original = objectify_and_remove_method(original_method)
mod = Module.new
mod.class_eval do
define_method(original_method.to_sym) do
changed; notify_observers(original_method, :before)
original.bind(self).call if original
changed; notify_observers(original_method, :after)
end
end
include mod
end
end
end
class MyObservedHouse
include SuperSimpleCallbacks
before :party, [:walk_dinosaure, :prepare, :just_idle]
after :party, [:just_idle, :keep_house, :walk_dinosaure]
before :home_office, [:just_idle, :prepare, :just_idle]
after :home_office, [:just_idle, :walk_dinosaure, :just_idle]
before :second_level, [:party]
def home_office
puts "learning and working with ruby...".upcase
end
def party
puts "having party...".upcase
end
def just_idle
puts "...."
end
def prepare
puts "preparing snacks..."
end
def keep_house
puts "house keeping..."
end
def walk_dinosaure
puts "walking the dinosaure..."
end
def second_level
puts "second level..."
end
end
MyObservedHouse.new.tap do |house|
puts "-------------------------"
puts "-- about calling party --"
puts "-------------------------"
house.party
puts "-------------------------------"
puts "-- about calling home_office --"
puts "-------------------------------"
house.home_office
puts "--------------------------------"
puts "-- about calling second_level --"
puts "--------------------------------"
house.second_level
end
# => ...
# -------------------------
# -- about calling party --
# -------------------------
# walking the dinosaure...
# preparing snacks...
# ....
# HAVING PARTY...
# ....
# house keeping...
# walking the dinosaure...
# -------------------------------
# -- about calling home_office --
# -------------------------------
# ....
# preparing snacks...
# ....
# LEARNING AND WORKING WITH RUBY...
# ....
# walking the dinosaure...
# ....
# --------------------------------
# -- about calling second_level --
# --------------------------------
# walking the dinosaure...
# preparing snacks...
# ....
# HAVING PARTY...
# ....
# house keeping...
# walking the dinosaure...
# second level...
This simple presentation of the use of Observable could be useful: http://www.oreillynet.com/ruby/blog/2006/01/ruby_design_patterns_observer.html
So, this may be very "un-ruby", and I am not a "professional" Ruby developer, so if you guys are going to smack be, be gentle please :)
Ruby has a built-int module called Observer. I have not found it easy to use, but to be fair I did not give it much of a chance. In my projects I have resorted to creating my own EventHandler type (yes, I use C# a lot). Here is the basic structure:
class EventHandler
def initialize
#client_map = {}
end
def add_listener(id, func)
(#client_map[id.hash] ||= []) << func
end
def remove_listener(id)
return #client_map.delete(id.hash)
end
def alert_listeners(*args)
#client_map.each_value { |v| v.each { |func| func.call(*args) } }
end
end
So, to use this I expose it as a readonly member of a class:
class Foo
attr_reader :some_value_changed
def initialize
#some_value_changed = EventHandler.new
end
end
Clients of the "Foo" class can subscribe to an event like this:
foo.some_value_changed.add_listener(self, lambda { some_func })
I am sure this is not idiomatic Ruby and I am just shoehorning my C# experience into a new language, but it has worked for me.
If you are willing to use ActiveSupport (from Rails), you have a straightforward implementation
class ObjectWithCallbackHooks
include ActiveSupport::Callbacks
define_callbacks :initialize # Your object supprots an :initialize callback chain
include ObjectWithCallbackHooks::Plugin
def initialize(*)
run_callbacks(:initialize) do # run `before` callbacks for :initialize
puts "- initializing" # then run the content of the block
end # then after_callbacks are ran
end
end
module ObjectWithCallbackHooks::Plugin
include ActiveSupport::Concern
included do
# This plugin injects an "after_initialize" callback
set_callback :initialize, :after, :initialize_some_plugin
end
end
I know this is an old post, but I found it when tried to solve a similar problem.
It's a really elegant solution, and most importantly, it can work with and without a callback.
Let's say we have the Arithmetic class which implements basic operations on them — addition and subtraction.
class Arithmetic
def addition(a, b)
a + b
end
def subtraction(a, b)
a - b
end
end
And we want to add a callback for each operation which will do something with the input data and result.
In the below example we will implement the after_operation method which accepts the Ruby block which will be executed after an operation.
class Arithmetic
def after_operation(&block)
#after_operation_callback = block
end
def addition(a, b)
do_operation('+', a, b)
end
def subtraction(a, b)
do_operation('-', a, b)
end
private
def do_operation(sign, a, b)
result =
case sign
when '+'
a + b
when '-'
a - b
end
if callback = #after_operation_callback
callback.call(sign, a, b, result)
end
result
end
end
Using with callback:
callback = -> (sign, a, b, result) do
puts "#{a} #{sign} #{b} = #{result}"
end
arithmetic = Arithmetic.new
arithmetic.after_operation(&callback)
puts arithmetic.addition(1, 2)
puts arithmetic.subtraction(3, 1)
Output:
1 + 2 = 3
3
3 - 1 = 2
2
I often implement callbacks in Ruby like in the following example. It's very comfortable to use.
class Foo
# Declare a callback.
def initialize
callback( :on_die_cast )
end
# Do some stuff.
# The callback event :on_die_cast is triggered.
# The variable "die" is passed to the callback block.
def run
while( true )
die = 1 + rand( 6 )
on_die_cast( die )
sleep( die )
end
end
# A method to define callback methods.
# When the latter is called with a block, it's saved into a instance variable.
# Else a saved code block is executed.
def callback( *names )
names.each do |name|
eval <<-EOF
##{name} = false
def #{name}( *args, &block )
if( block )
##{name} = block
elsif( ##{name} )
##{name}.call( *args )
end
end
EOF
end
end
end
foo = Foo.new
# What should be done when the callback event is triggered?
foo.on_die_cast do |number|
puts( number )
end
foo.run
I know this is an old post, but others that come across this may find my solution helpful.
http://chrisshepherddev.blogspot.com/2015/02/callbacks-in-pure-ruby-prepend-over.html

Resources