I have several classes and I want each one to maintain on the class level a hash of all the instances that have been created for future lookup. Something akin to:
class A
def initialize(id, otherstuff)
# object creation logic
##my_hash[id]=self
end
def self.find(id)
##my_hash[id]
end
end
so I can then A.find(id) and get the right instance back.
There are several of these classes (A, B, etc), all having ids, all of which I want to have this functionality.
Can I have them all inherit from a superclass which has a generic version of this which they can leverage so I don't have to reimplement many things for every class?
Yes, you can either inherit from the same superclass, or use modules and include:
module M
def initialize(id)
##all ||= {}
##all[id] = self
end
def print
p ##all
end
end
class C
include M
def initialize(id)
super
puts "C instantiated"
end
end
If you want to keep separate indexes for each subclass, you can do something like:
def initialize(id)
##all ||= {}
##all[self.class] ||= {}
##all[self.class][id] = self
end
Edit: After your comment, I see that you need to keep per-class indexes. So:
class A
def initialize(id)
self.class.index(id, self)
end
def self.index id, instance
#all ||= {}
#all[id] = instance
end
def self.find(id)
#all[id]
end
end
class B < A
end
class C < A
end
a = A.new(1)
b = B.new(2)
c = C.new(3)
p A.find(1)
#=> #<A:0x10016c190>
p B.find(2)
#=> #<B:0x10016c140>
p C.find(3)
#=> #<C:0x10016c118>
p A.find(2)
#=> nil
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>
I am building an in-memory instance model in Ruby. There are a bunch of classes that each get instantiated and managed by class methods on that class. There are a bunch of those class methods, e.g. list all instances, retrieve all instances, etc.
The code for these methods is common across all classes and does not need to take any account of any particularities of those classes. Hence, I would like that code to live in a common place. See the list method below. My question: How to best achieve this.
class A
attr_reader :value
##instances = []
def initialize(value:)
#value = value; ##instances << self
end
def self.list
##instances.each { |i| puts "#{i.value}"}
end
end
class B
attr_reader :value
##instances = []
def initialize(value:)
#value = value; ##instances << self
end
def self.list
##instances.each { |i| puts "#{i.value}"}
end
end
A.new(value: '100')
A.new(value: '101')
B.new(value: '200')
B.new(value: '201')
A.list
B.list
Ideally, I define the list method only once. I have also tried moving that to a super-class:
class Entity
def self.list
##instances.each { |i| puts "AB: #{i.value}"}
end
end
class A < Entity
attr_reader :value
##instances = []
def initialize(value:)
#value = value; ##instances << self
end
end
class B < Entity
attr_reader :value
##instances = []
def initialize(value:)
#value = value; ##instances << self
end
end
...but as one would expect the super-class cannot access the ##instances array of its sub-classes. Moving the ##instances array to the super-class results in the array being common to all classes, which is not what I need.
The main change you need to make is to use class instance variables rather than class variables. For reasons explained here class variables should be used sparingly; class instance variables are generally a better choice, as is illustrated nicely by this question.
class Entity
attr_reader :value
class << self
attr_reader :ins
end
def self.inherited(klass)
klass.instance_variable_set(:#ins, [])
end
def initialize(value:)
#value = value
self.class.ins << self
end
def self.list
#ins.each { |i| puts "#{i.value}"}
end
end
class A < Entity; end
class B < Entity; end
A.new(value: '100')
#=> #<A:0x00005754a59dc640 #value="100">
A.new(value: '101')
#=> #<A:0x00005754a59e4818 #value="101">
A.list
# 100
# 101
B.new(value: '200')
#=> #<B:0x00005754a59f0910 #value="200">
B.new(value: '201')
#=> #<B:0x00005754a59f8b88 #value="201">
B.list
# 200
# 201
I defined a getter for the class instance variable #ins in Entity's singleton class1:
class << self
attr_reader :ins
end
When subclasses of Entity are created the callback method Class::inherited is executed on Entity, passing as an argument the class that has been created. inherited creates and initializes (to an empty array) the class instance variable #ins for the class created.
Another way of doing that, without using a callback method, is as follows.
class Entity
attr_reader :value
class << self
attr_accessor :ins
end
def initialize(value:)
#value = value
(self.class.ins ||= []) << self
end
def self.list
#ins.each { |i| puts "#{i.value}"}
end
end
The fragment:
(self.class.ins ||= [])
sets #ins to an empty array if #ins equals nil. If #ins is referenced before it is created, nil is returned, so either way, #ins is set equal to []. In order to execute this statement I needed to change attr_reader :ins to attr_accessor :ins in order to perform the assignment #ins = [] (though I could have used instance_variable_set instead).
Note that if I were to add the line #ins = [] to Entity (as th first line, say), the instance variable #ins would be created for every subclass when the subclass is created, but that instance variable would not be initialized to an empty array, so that line would serve no purpose.
1. Alternatively, one could write, singleton_class.public_send(:attr_reader, :ins).
I have a ruby class, and in one of the methods, it calls an external function, and pass in all instance variables, and continue with the return value. Here is the code:
class MyClass
attr_accessor :name1
attr_accessor :name2
...
attr_accessor :namen
def inner_func():
all_vars = ???? # how to collect all my instance variables into a dict/Hash?
res = out_func(all_vars)
do_more_stuff(res)
end
end
The problem is the instance variables might vary in subclasses. I can't refer them as their names. So, is there a way to do this? Or Am I thinking in a wrong way?
You can use instance_variables to collect them in an Array. You will get all initialized instance variables.
class MyClass
attr_accessor :name1
attr_accessor :name2
...
attr_accessor :namen
def inner_func():
all_vars = instance_variables
res = out_func(all_vars)
do_more_stuff(res)
end
end
You could keep track of all accessors as you create them:
class Receiver
def work(arguments)
puts "Working with #{arguments.inspect}"
end
end
class MyClass
def self.attr_accessor(*arguments)
super
#__attribute_names__ ||= []
#__attribute_names__ += arguments
end
def self.attribute_names
#__attribute_names__
end
def self.inherited(base)
parent = self
base.class_eval do
#__attribute_names__ = parent.attribute_names
end
end
def attributes
self.class.attribute_names.each_with_object({}) do |attribute_name, result|
result[attribute_name] = public_send(attribute_name)
end
end
def work
Receiver.new.work(attributes)
end
attr_accessor :foo
attr_accessor :bar
end
class MySubclass < MyClass
attr_accessor :baz
end
Usage
my_class = MyClass.new
my_class.foo = 123
my_class.bar = 234
my_class.work
# Working with {:foo=>123, :bar=>234}
my_subclass = MySubclass.new
my_subclass.foo = 123
my_subclass.bar = 234
my_subclass.baz = 345
my_subclass.work
# Working with {:foo=>123, :bar=>234, :baz=>345}
I want to call instance_eval on this class:
class A
attr_reader :att
end
passing this method b:
class B
def b(*args)
att
end
end
but this is happening:
a = A.new
bb = B.new
a.instance_eval(&bb.method(:b)) # NameError: undefined local variable or method `att' for #<B:0x007fb39ad0d568>
When b is a block it works, but b as a method isn't working. How can I make it work?
It's not clear exactly what you goal is. You can easily share methods between classes by defining them in a module and including the module in each class
module ABCommon
def a
'a'
end
end
class A
include ABCommon
end
Anything = Hash
class B < Anything
include ABCommon
def b(*args)
a
end
def run
puts b
end
end
This answer does not use a real method as asked, but I didn't need to return a Proc or change A. This is a DSL, def_b should have a meaningful name to the domain, like configure, and it is more likely to be defined in a module or base class.
class B
class << self
def def_b(&block)
(#b_blocks ||= []) << block
end
def run
return if #b_blocks.nil?
a = A.new
#b_blocks.each { |block| a.instance_eval(&block) }
end
end
def_b do
a
end
end
And it accepts multiple definitions. It could be made accept only a single definition like this:
class B
class << self
def def_b(&block)
raise "b defined twice!" unless #b_block.nil?
#b_block = block
end
def run
A.new.instance_eval(&#b_block) unless #b_block.nil?
end
end
def_b do
a
end
end
I have a module M which I want to tag specific methods as "special", in such a way that classes which mix in this module can check whether a given method name is special. This is what I've tried:
module M
def specials
#specials ||= {}
end
def self.special name
specials[name] = true
end
def is_special? name
specials[name]
end
def meth1
...
end
special :meth1
end
class C
include M
def check name
is_special? name
end
end
Of course this doesn't work, because I can't call an instance method from the class method self.special. I suspect that if I want to keep the feature of being able to call special :<name> below the wanted methods in the module, I have no choice but to use class variables (e.g. ##specials) Can somebody prove me wrong?
You can make all these methods class methods and do the following:
module M
def self.specials
#specials ||= {}
end
def self.special name
self.specials[name] = true
end
def self.is_special? name
self.specials[name]
end
def meth1
'foo'
end
def meth2
'bar'
end
special :meth1
end
class C
include M
def check name
M.is_special? name
end
end
p C.new.check(:meth1)
#=> true
p C.new.check(:meth2)
#=> nil
Not sure if that would work for you.