I have to write a my_initialize method in class Class, so that it works in this manor, when used in another class:
class Person
my_initialize :name, :surname
end
is equivalent to :
class Person
def initialize(name, surname)
#name, #surname = name, surname
end
end
It also has to raise an ArgumentError if a wrong number of arguments is passed. For example Person.new("Mickey") is invalid. I know that my code should look something like:
class Class
def my_initialize(*args)
args.each do |arg|
self.class_eval("?????")
end
end
end
I just started to read metaprogramming, but can't find anything useful for my problem. Any ideas how to do this task?
class Class
def my_initialize(*vars)
define_method :initialize do |*args|
if args.length != vars.length
raise ArgumentError, 'wrong number of arguments'
end
vars.zip(args).each do |var, arg|
instance_variable_set :"##{var}", arg
end
end
end
end
class C
my_initialize :a, :b
end
The Module#define_method method takes a method name and block and defines the method for that module. In this case, the module is C. The Object#instance_variable_set method takes an instance variable name and a value and sets it. The instance of Object in this case would be an instance of C.
By the way, it is best to avoid using methods where you pass a string of code in to be evaluated. I would recommend passing blocks instead.
Here's another way that does not use define_method.
class Class
def my_initialize(*vars)
str = "def initialize(*args)
raise ArgumentError if args.size != #{vars.size}
#{vars}.zip(args).each do |var, arg|
instance_variable_set(\"#\#{var}\", arg)
end
end"
class_eval str
end
end
class C
my_initialize :a, :b
end
c = C.new("Betty", "Boop")
#=> #<C:0x00000102805428 #a="Betty", #b="Boop">
C.private_instance_methods(false)
#=> [:initialize]
c.instance_variables
#=> [:#a, :#b]
C.new("Betty")
#=> ArgumentError
Related
I'm working to create a few Ruby builder objects, and thinking on how I could reuse some of Ruby's magic to reduce the logic of the builder to a single class/module. It's been ~10 years since my last dance with the language, so a bit rusty.
For example, I have this builder:
class Person
PROPERTIES = [:name, :age]
attr_accessor(*PROPERTIES)
def initialize(**kwargs)
kwargs.each do |k, v|
self.send("#{k}=", v) if self.respond_to?(k)
end
end
def build
output = {}
PROPERTIES.each do |prop|
if self.respond_to?(prop) and !self.send(prop).nil?
value = self.send(prop)
# if value itself is a builder, evalute it
output[prop] = value.respond_to?(:build) ? value.build : value
end
end
output
end
def method_missing(m, *args, &block)
if m.to_s.start_with?("set_")
mm = m.to_s.gsub("set_", "")
if PROPERTIES.include?(mm.to_sym)
self.send("#{mm}=", *args)
return self
end
end
end
end
Which can be used like so:
Person.new(name: "Joe").set_age(30).build
# => {name: "Joe", age: 30}
I would like to be able to refactor everything to a class and/or module so that I could create multiple such builders that'll only need to define attributes and inherit or include the rest (and possibly extend each other).
class BuilderBase
# define all/most relevant methods here for initialization,
# builder attributes and object construction
end
module BuilderHelper
# possibly throw some of the methods here for better scope access
end
class Person < BuilderBase
include BuilderHelper
PROPERTIES = [:name, :age, :email, :address]
attr_accessor(*PROPERTIES)
end
# Person.new(name: "Joe").set_age(30).set_email("joe#mail.com").set_address("NYC").build
class Server < BuilderBase
include BuilderHelper
PROPERTIES = [:cpu, :memory, :disk_space]
attr_accessor(*PROPERTIES)
end
# Server.new.set_cpu("i9").set_memory("32GB").set_disk_space("1TB").build
I've been able to get this far:
class BuilderBase
def initialize(**kwargs)
kwargs.each do |k, v|
self.send("#{k}=", v) if self.respond_to?(k)
end
end
end
class Person < BuilderBase
PROPERTIES = [:name, :age]
attr_accessor(*PROPERTIES)
def build
...
end
def method_missing(m, *args, &block)
...
end
end
Trying to extract method_missing and build into the base class or a module keeps throwing an error at me saying something like:
NameError: uninitialized constant BuilderHelper::PROPERTIES
OR
NameError: uninitialized constant BuilderBase::PROPERTIES
Essentially the neither the parent class nor the mixin are able to access the child class' attributes. For the parent this makes sense, but not sure why the mixin can't read the values inside the class it was included into. This being Ruby I'm sure there's some magical way to do this that I have missed.
Help appreciated - thanks!
I reduced your sample to the required parts and came up with:
module Mixin
def say_mixin
puts "Mixin: Value defined in #{self.class::VALUE}"
end
end
class Parent
def say_parent
puts "Parent: Value defined in #{self.class::VALUE}"
end
end
class Child < Parent
include Mixin
VALUE = "CHILD"
end
child = Child.new
child.say_mixin
child.say_parent
This is how you could access a CONSTANT that lives in the child/including class from the parent/included class.
But I don't see why you want to have this whole Builder thing in the first place. Would an OpenStruct not work for your case?
Interesting question. As mentioned by #Pascal, an OpenStruct might already do what you're looking for.
Still, it might be more concise to explicitly define the setter methods. It might also be clearer to replace the PROPERTIES constants by methods calls. And since I'd expect a build method to return a complete object and not just a Hash, I renamed it to to_h:
class BuilderBase
def self.properties(*ps)
ps.each do |property|
attr_reader property
define_method :"set_#{property}" do |value|
instance_variable_set(:"##{property}", value)
#hash[property] = value
self
end
end
end
def initialize(**kwargs)
#hash = {}
kwargs.each do |k, v|
self.send("set_#{k}", v) if self.respond_to?(k)
end
end
def to_h
#hash
end
end
class Person < BuilderBase
properties :name, :age, :email, :address
end
p Person.new(name: "Joe").set_age(30).set_email("joe#mail.com").set_address("NYC").to_h
# {:name=>"Joe", :age=>30, :email=>"joe#mail.com", :address=>"NYC"}
class Server < BuilderBase
properties :cpu, :memory, :disk_space
end
p Server.new.set_cpu("i9").set_memory("32GB").set_disk_space("1TB").to_h
# {:cpu=>"i9", :memory=>"32GB", :disk_space=>"1TB"}
I think no need to declare PROPERTIES, we can create a general builder like this:
class Builder
attr_reader :build
def initialize(clazz)
#build = clazz.new
end
def self.build(clazz, &block)
builder = Builder.new(clazz)
builder.instance_eval(&block)
builder.build
end
def set(attr, val)
#build.send("#{attr}=", val)
self
end
def method_missing(m, *args, &block)
if #build.respond_to?("#{m}=")
set(m, *args)
else
#build.send("#{m}", *args, &block)
end
self
end
def respond_to_missing?(method_name, include_private = false)
#build.respond_to?(method_name) || super
end
end
Using
class Test
attr_accessor :x, :y, :z
attr_reader :w, :u, :v
def set_w(val)
#w = val&.even? ? val : 0
end
def add_u(val)
#u = val if val&.odd?
end
end
test1 = Builder.build(Test) {
x 1
y 2
z 3
} # <Test:0x000055b6b0fb2888 #x=1, #y=2, #z=3>
test2 = Builder.new(Test).set(:x, 1988).set_w(6).add_u(2).build
# <Test:0x000055b6b0fb23b0 #x=1988, #w=6>
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.
Is there are any possibility to get name of the anonymous class in the inherited, and not raise "fail A"? Should be made through Class object creation (no eval or similar).
class A
def self.inherited(base)
raise 'fail A' unless base.name
end
end
B = Class.new(A)
# or
Object.const_set :B, Class.new(A)
The code above doesn't work, because anonymous class isn't yet initialized so it cannot be set to a specific constant.
No.
An anonymous class doesn’t have a name until it’s been assigned to a constant (e.g. (B = Class.new).name #=> "B"). Since assignment does not happen until after the class instance has been created (during which hooks—including inherited—are called), there’s no way you can get the name until afterwards.
What about something like:
class Superclass
def self.inherited(base)
raise 'Invalid class name' unless #forced_anonymous_subclass_name == :A
end
def self.forced_anonymous_subclass_name
#forced_anonymous_subclass_name
end
def self.with_forced_anonymous_subclass_name(class_name)
#forced_anonymous_subclass_name = class_name
yield
ensure
#forced_anonymous_subclass_name = nil
end
end
sc = Superclass
sc.with_forced_anonymous_subclass_name(:A) do
Object.const_set sc.forced_anonymous_subclass_name, Class.new(sc)
end #=> A
sc.with_forced_anonymous_subclass_name(:B) do
Object.const_set sc.forced_anonymous_subclass_name, Class.new(sc)
end #=> RuntimeError
Feel free to ask if unclear/improvements/etc.
To be clear - this code is running perfectly - code with proc
but if instead I change Proc.new to lambda, I'm getting an error
ArgumentError: wrong number of arguments (1 for 0)
May be this is because instance_eval wants to pass self as a param, and lambda treats as a method and do not accept unknown params?
There is two examples - first is working:
class Rule
def get_rule
Proc.new { puts name }
end
end
class Person
attr_accessor :name
def init_rule
#name = "ruby"
instance_eval(&Rule.new.get_rule)
end
end
second is not:
class Rule
def get_rule
lambda { puts name }
end
end
class Person
attr_accessor :name
def init_rule
#name = "ruby"
instance_eval(&Rule.new.get_rule)
end
end
Thanks
You are actually correct in your assumption. Self is being passed to the Proc and to the lambda as it is being instance_eval'ed. A major difference between Procs and lambdas is that lambdas check the arity of the block being being passed to them.
So:
class Rule
def get_rule
lambda { |s| puts s.inspect; puts name; }
end
end
class Person
attr_accessor :name
def init_rule
#name = "ruby"
instance_eval(&Rule.new.get_rule)
end
end
p = Person.new
p.init_rule
#<Person:0x007fd1099f53d0 #name="ruby">
ruby
Here I told the lambda to expect a block with arity 1 and as you see in the argument inspection, the argument is indeed the self instance of Person class.
Given the following class:
class Test
attr_accessor :name
end
When I create the object, I want to do the following:
t = Test.new {name = 'Some Test Object'}
At the moment, it results in the name attribute still being nil.
Is that possible without adding an initializer?
ok,
I came up with a solution. It uses the initialize method but on the other hand do exactly what you want.
class Test
attr_accessor :name
def initialize(init)
init.each_pair do |key, val|
instance_variable_set('#' + key.to_s, val)
end
end
def display
puts #name
end
end
t = Test.new :name => 'hello'
t.display
happy ? :)
Alternative solution using inheritance. Note, with this solution, you don't need to explicitly declare the attr_accessor!
class CSharpStyle
def initialize(init)
init.each_pair do |key, val|
instance_variable_set('#' + key.to_s, val)
instance_eval "class << self; attr_accessor :#{key.to_s}; end"
end
end
end
class Test < CSharpStyle
def initialize(arg1, arg2, *init)
super(init.last)
end
end
t = Test.new 'a val 1', 'a val 2', {:left => 'gauche', :right => 'droite'}
puts "#{t.left} <=> #{t.right}"
As mentioned by others, the easiest way to do this would be to define an initialize method. If you don't want to do that, you could make your class inherit from Struct.
class Test < Struct.new(:name)
end
So now:
>> t = Test.new("Some Test Object")
=> #<struct Test name="Some Test Object">
>> t.name
=> "Some Test Object"
There is a general way of doing complex object initialization by
passing a block with necessary actions. This block is evaluated in the
context of the object to be initialized, so you have an easy access to
all instance variables and methods.
Continuing your example, we can define this generic initializer:
class Test
attr_accessor :name
def initialize(&block)
instance_eval(&block)
end
end
and then pass it the appropriate code block:
t = Test.new { #name = 'name' }
or
t = Test.new do
self.name = 'name'
# Any other initialization code, if needed.
end
Note that this approach does not require adding much complexity
to the initialize method, per se.
As previously mentioned, the sensible way to do this is either with a Struct or by defining an Test#initialize method. This is exactly what structs and constructors are for. Using an options hash corresponding to attributes is the closest equivalent of your C# example, and it's a normal-looking Ruby convention:
t = Test.new({:name => "something"})
t = Test.new(name: "something") # json-style or kwargs
But in your example you are doing something that looks more like variable assignment using = so let's try using a block instead of a hash. (You're also using Name which would be a constant in Ruby, we'll change that.)
t = Test.new { #name = "something" }
Cool, now let's make that actually work:
class BlockInit
def self.new(&block)
super.tap { |obj| obj.instance_eval &block }
end
end
class Test < BlockInit
attr_accessor :name
end
t = Test.new { #name = "something" }
# => #<Test:0x007f90d38bacc0 #name="something">
t.name
# => "something"
We've created a class with a constructor that accepts a block argument, which is executed within the newly-instantiated object.
Because you said you wanted to avoid using initialize, I'm instead overriding new and calling super to get the default behavior from Object#new. Normally we would define initialize instead, this approach isn't recommended except in meeting the specific request in your question.
When we pass a block into a subclass of BlockInit we can do more than just set variable... we're essentially just injecting code into the initialize method (which we're avoiding writing). If you also wanted an initialize method that does other stuff (as you mentioned in comments) you could add it to Test and not even have to call super (since our changes aren't in BlockInit#initialize, rather BlockInit.new)
Hope that's a creative solution to a very specific and intriguing request.
The code you're indicating is passing parameters into the initialize function. You will most definitely have to either use initialize, or use a more boring syntax:
test = Test.new
test.name = 'Some test object'
Would need to subclass Test (here shown with own method and initializer) e.g.:
class Test
attr_accessor :name, :some_var
def initialize some_var
#some_var = some_var
end
def some_function
"#{some_var} calculation by #{name}"
end
end
class SubClassedTest < Test
def initialize some_var, attrbs
attrbs.each_pair do |k,v|
instance_variable_set('#' + k.to_s, v)
end
super(some_var)
end
end
tester = SubClassedTest.new "some", name: "james"
puts tester.some_function
outputs: some calculation by james
You could do this.
class Test
def not_called_initialize(but_act_like_one)
but_act_like_one.each_pair do |variable,value|
instance_variable_set('#' + variable.to_s, value)
class << self
self
end.class_eval do
attr_accessor variable
end
end
end
end
(t = Test.new).not_called_initialize :name => "Ashish", :age => 33
puts t.name #=> Ashish
puts t.age #=> 33
One advantage is that you don't even have to define your instance variables upfront using attr_accessor. You could pass all the instance variables you need through not_called_initialize method and let it create them besides defining the getters and setters.
If you don't want to override initialize then you'll have to move up the chain and override new. Here's an example:
class Foo
attr_accessor :bar, :baz
def self.new(*args, &block)
allocate.tap do |instance|
if args.last.is_a?(Hash)
args.last.each_pair do |k,v|
instance.send "#{k}=", v
end
else
instance.send :initialize, *args
end
end
end
def initialize(*args)
puts "initialize called with #{args}"
end
end
If the last thing you pass in is a Hash it will bypass initialize and call the setters immediately. If you pass anything else in it will call initialize with those arguments.