Ruby method chaining with an Enumerable class - ruby

I'm attempting to adapt the method-chaining example cited in this posting (Method chaining and lazy evaluation in Ruby) to work with an object that implements the Enumerable class (Implement a custom Enumerable collection class in Ruby )
Coffee class:
class Coffee
attr_accessor :name
attr_accessor :strength
def initialize(name, strength)
#name = name
#strength = strength
end
def <=>(other_coffee)
self.strength <=> other_coffee.strength
end
def to_s
"<name: #{name}, strength: #{strength}>"
end
end
Criteria class:
class Criteria
def initialize(klass)
#klass = klass
end
def criteria
#criteria ||= {:conditions => {}}
end
# only show coffee w/ this strength
def strength(strength)
criteria[:strength] = strength
self
end
# if there are multiple coffees, choose the first n=limit
def limit(limit)
criteria[:limit] = limit
self
end
# allow collection enumeration
def each(&block)
#klass.collection.select { |c| c[:strength] == criteria[:strength] }.each(&block)
end
end
CoffeeShop class:
class CoffeeShop
include Enumerable
def self.collection
#collection=[]
#collection << Coffee.new("Laos", 10)
#collection << Coffee.new("Angkor", 7)
#collection << Coffee.new("Nescafe", 1)
end
def self.limit(*args)
Criteria.new(self).limit(*args)
end
def self.strength(*args)
Criteria.new(self).strength(*args)
end
end
When I run this code:
CoffeeShop.strength(10).each { |c| puts c.inspect }
I get an error:
criteria.rb:32:in block in each': undefined method '[]' for #<Coffee:0x007fd25c8ec520 #name="Laos", #strength=10>
I'm certain that I haven't defined the Criteria.each method correctly, but I'm not sure how to correct it. How do I correct this?
Moreover, the each method doesn't support the limit as currently written. Is there a better way to filter the array such that it is easier to support both the strength and limit?
Other coding suggestions are appreciated.

Your Coffee class defines method accessors for name and strength. For a single coffee object, you can thus get the attributes with
coffee.name
# => "Laos"
coffee.strength
# => 10
In your Criteria#each method, you try to access the attributes using the subscript operator, i.e. c[:strength] (with c being an Instance of Coffee in this case). Now, on your Coffee class, you have not implemented the subscript accessor which resulting in the NoMethodError you see there.
You could thus either adapt your Criteria#each method as follows:
def each(&block)
#klass.collection.select { |c| c.strength == criteria[:strength] }.each(&block)
end
or you could implement the subscript operators on your Coffee class:
class Coffee
attr_accessor :name
attr_accessor :strength
# ...
def [](key)
public_send(key)
end
def []=(key, value)
public_send(:"#{key}=", value)
end
end
Noe, as an addendum, you might want to extend your each method in any case. A common (and often implicitly expected) pattern is that methods like each return an Enumerator if no block was given. This allows patterns like CoffeeShop.strength(10).each.group_by(&:strength).
You can implement this b a simple on-liner in your method:
def each(&block)
return enum_for(__method__) unless block_given?
#klass.collection.select { |c| c.strength == criteria[:strength] }.each(&block)
end

Related

Creating Ruby builder object with re-usable code

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>

Ruby equivalent of lisp-like "apply"?

I would like to create an instance method that takes another instance method of its own class as a parameter, and then applies the passed method on the instance it's working on (known as self):
class MyClass
attr_reader :called_methods
def initialize
#called_methods = []
end
def my_first_method!
#called_methods << :my_first_method
self
end
def my_second_method!
#called_methods << :my_second_method
self
end
def my_strange_method!(secondary)
# Want to apply method whose name is given by secondary, to self
end
end
p MyClass.new.my_second_method!.my_strange_method!(:my_first_method!).called_methods
I suspect the unary & may be key, but all the web pages I can find on that operator involve calling methods on multiple objects, as when iterating over an Enumerable with #each or #map.
Use Object#public_send (or Object#send to apply protected/private method).
def my_strange_method!(secondary)
public_send(secondary)
self
end
p MyClass.new.
my_second_method!.
my_strange_method!(:my_first_method!).
called_methods
#⇒ [:my_second_method, :my_first_method]
There could be more defensive way to apply if and only the method is known:
def my_strange_method!(secondary)
raise ArgumentError.new("Unknown method #{secondary}") \
unless methods.include? secondary.to_s.to_sym
public_send(secondary)
end
p MyClass.new.
my_second_method!.
my_strange_method!(:my_first_method!).
called_methods
#⇒ [:my_second_method, :my_first_method]
p MyClass.new.
my_second_method!.
my_strange_method!(:inexisting_method!).
called_methods
#⇒ ArgumentError: Unknown method inexisting_method!
This is tagged with functional-programming so I'm going to offer a persistent (immutable) design -
class MyClass
attr_reader :called_methods
def initialize(m = [])
#called_methods = m
end
def my_first_method!
MyClass.new(called_methods + [ :first ])
end
def my_second_method!
MyClass.new(called_methods + [ :second ])
end
def my_strange_method!(secondary)
public_send secondary
end
end
MyClass.new.my_second_method!.my_strange_method!(:my_first_method!).called_methods
# [:second, :first]

Why is this ruby method not being defined in my class?

Here's the code:
module Dog
class Breed < Animal::Base
class << self
def all
get '/v1/breeds'
end
def find(hashed_id)
get "/v1/breeds/#{breed_id}"
end
end
def bark
"woof"
end
end
end
And for the base:
module Dog
class Base < ActiveRecord::Base
include HTTParty
base_uri 'https://api.dogs.com'
format :json
default_params api_password: ENV['ANIMAL_PASSWORD']
end
end
module HTTParty
module ClassMethods
def get(path, options = {}, &block)
response = perform_request(Net::HTTP::Get, path, options, &block)
if response.is_a? Array
methodize_array response
elsif response.is_a? Hash
new_ros response
end
end
def methodize_array(response)
array = []
response.each do |res|
array << new_ros(res)
end
array
end
private
def new_ros(object)
RecursiveOpenStruct.new(object, recurse_over_arrays: true)
end
end
end
This is a silly example, but it should work in theory. What happens is is that we grab some data from an API. When that data is grabbed, we discover that its a Hash. We don't like Hashes, so we reopen the get request within HTTParty and have it perform a recursive open struct to make it an object.
We perform this get as Dog::Breed.all. We receive an array that, thankfully to ROS, was converted to an object.
Now, when I call Dog::Breed.all.bark it doesn't work:
undefined method `bark' for #<Array:0x007fc7acbb6108>
If I make it:
def self.bark
"woof"
end
And then call Dog::Breed.bark, it will woof at me. How do I make it so that I can add methods to the Breed class so that I can do Dog::Breed.all.bark or Dog::Breed.find(2).bark?
The output from Dog::Breed.all was a #<RecursiveOpenStruct>. Disclaimer: That was an example case, not real life, dog.com leads to petsmart.
Dog::Breed.all returns an Array of Breed, not Breed. If you want all dogs to bark you need to iterate over the array, and make each one bark:
Dog::Breed.all.each(&:bark)

How can one set property values when initializing an object in Ruby?

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.

Best Way to Abstract Initializing Attributes

What's the best way to abstract this pattern:
class MyClass
attr_accessor :foo, :bar
def initialize(foo, bar)
#foo, #bar = foo, bar
end
end
A good solution should take superclasses into consideration and be able to handle still being able to have an initializer to do more things. Extra points for not sacrificing performance in your solution.
A solution to that problem already (partially) exists, but if you want a more declarative approach in your classes then the following should work.
class Class
def initialize_with(*attrs, &block)
attrs.each do |attr|
attr_accessor attr
end
(class << self; self; end).send :define_method, :new do |*args|
obj = allocate
init_args, surplus_args = args[0...attrs.size], args[attrs.size..-1]
attrs.zip(init_args) do |attr, arg|
obj.instance_variable_set "##{attr}", arg
end
obj.send :initialize, *surplus_args
obj
end
end
end
You can now do:
class MyClass < ParentClass
initialize_with :foo, :bar
def initialize(baz)
#initialized = true
super(baz) # pass any arguments to initializer of superclass
end
end
my_obj = MyClass.new "foo", "bar", "baz"
my_obj.foo #=> "foo"
my_obj.bar #=> "bar"
my_obj.instance_variable_get(:#initialized) #=> true
Some characteristics of this solution:
Specify constructor attributes with initialize_with
Optionally use initialize to do custom initialization
Possible to call super in initialize
Arguments to initialize are the arguments that were not consumed by attributes specified with initialize_with
Easily extracted into a Module
Constructor attributes specified with initialize_with are inherited, but defining a new set on a child class will remove the parent attributes
Dynamic solution probably has performance hit
If you want to create a solution with absolute minimal performance overhead, it would be not that difficult to refactor most of the functionality into a string which can be evaled when the initializer is defined. I have not benchmarked what the difference would be.
Note: I found that hacking new works better than hacking initialize. If you define initialize with metaprogramming, you'd probably get a scenario where you pass a block to initialize_with as a substitute initializer, and it's not possible to use super in a block.
This is the first solution that comes to my mind. There's one big downside in my module: you must define the class initialize method before including the module or it won't work.
There's probably a better solution for that problem, but this is what I wrote in less than a couple of minutes.
Also, I didn't keep performances too much into consideration. You probably can find a much better solution than me, especially talking about performances. ;)
#!/usr/bin/env ruby -wKU
require 'rubygems'
require 'activesupport'
module Initializable
def self.included(base)
base.class_eval do
extend ClassMethods
include InstanceMethods
alias_method_chain :initialize, :attributes
class_inheritable_array :attr_initializable
end
end
module ClassMethods
def attr_initialized(*attrs)
attrs.flatten.each do |attr|
attr_accessor attr
end
self.attr_initializable = attrs.flatten
end
end
module InstanceMethods
def initialize_with_attributes(*args)
values = args.dup
self.attr_initializable.each do |attr|
self.send(:"#{attr}=", values.shift)
end
initialize_without_attributes(values)
end
end
end
class MyClass1
attr_accessor :foo, :bar
def initialize(foo, bar)
#foo, #bar = foo, bar
end
end
class MyClass2
def initialize(*args)
end
include Initializable
attr_initialized :foo, :bar
end
if $0 == __FILE__
require 'test/unit'
class InitializableTest < Test::Unit::TestCase
def test_equality
assert_equal MyClass1.new("foo1", "bar1").foo, MyClass2.new("foo1", "bar1").foo
assert_equal MyClass1.new("foo1", "bar1").bar, MyClass2.new("foo1", "bar1").bar
end
end
end
class MyClass < Struct.new(:foo, :bar)
end
I know this is an old question with perfectly acceptable answers but I wanted to post my solution as it takes advantage of Module#prepend (new in Ruby 2.2) and the fact that modules are also classes for very simple solution. First the module to make the magic:
class InitializeWith < Module
def initialize *attrs
super() do
define_method :initialize do |*args|
attrs.each { |attr| instance_variable_set "##{attr}", args.shift }
super *args
end
end
end
end
Now let's use our fancy module:
class MyClass
prepend InitializeWith.new :foo, :bar
end
Note that I left our the attr_accessible stuff as I consider that a separate concern although it would be trivial to support. Now I can create an instance with:
MyClass.new 'baz', 'boo'
I can still define an initialize for custom initialization. If my custom initialize take an argument those will be any extra arguments provided to the new instance. So:
class MyClass
prepend InitializeWith.new :foo, :bar
def initialize extra
puts extra
end
end
MyClass.new 'baz', 'boo', 'dog'
In the above example #foo='baz', #bar='boo' and it will print dog.
What I also like about this solution is that it doesn't pollute the global namespace with a DSL. Objects that want this functionality can prepend. Everybody else is untouched.
This module allows an attrs hash as an option to new(). You can include the module in a class with inheritance, and the constructor still works.
I like this better than a list of attr values as parameters, because, particularly with inherited attrs, I wouldn't like trying to remember which param was which.
module Attrize
def initialize(*args)
arg = args.select{|a| a.is_a?(Hash) && a[:attrs]}
if arg
arg[0][:attrs].each do |key, value|
self.class.class_eval{attr_accessor(key)} unless respond_to?(key)
send(key.to_s + '=', value)
end
args.delete(arg[0])
end
(args == []) ? super : super(*args)
end
end
class Hue
def initialize(transparent)
puts "I'm transparent" if transparent
end
end
class Color < Hue
include Attrize
def initialize(color, *args)
p color
super(*args)
p "My style is " + #style if #style
end
end
And you can do this:
irb(main):001:0> require 'attrize'
=> true
irb(main):002:0> c = Color.new("blue", false)
"blue"
=> #<Color:0x201df4>
irb(main):003:0> c = Color.new("blue", true, :attrs => {:style => 'electric'})
"blue"
I'm transparent
"My style is electric"

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