Abstractable

Overview

Abstractable is Library for define abstract method.
Can know unimplemented abstract methods by fail fast as possible.
This mechanism is very useful for prevent the implementation leakage.

require "abstractable"
class AbstractDriver
  extend Abstractable
  abstract :open, :close
end

class AbstractIODriver < AbstractDriver
  abstract :read, :write
end

class NotImplIODriver < AbstractIODriver; end

NotImplIODriver.new
# => following abstract methods are not implemented. (NotImplementedError)
#    [:open, :close] defined in AbstractDriver
#    [:read, :write] defined in AbstractIODriver

See sample above. error occurred at call new method.
Info of unimplemented abstract method have been included in the error message.

Installation

gem install abstractable

How to use

First, call require "abstractable".
Then, extend Abstractable.

require "abstractable"
class AbstractClass
  extend Abstractable
end

Note: This document omit the require "abstractable" from now on.

Define abstract method

1. Specify Symbol (can specify multiple)

   class AbstractList
     extend Abstractable
   
     abstract :add, :insert, :empty?
   end
   

   If want to express the arguments then can write be as follows.

   class AbstractList
     extend Abstractable
   
     def add(value); end
     def insert(index, value); end
     def empty?; end
   
     abstract :add, :insert, :empty?
   end
   

2. In block
   Defined methods in block is all treated as an abstract method.

   class AbstractList
     extend Abstractable
   
     abstract do
       def add(value); end
       def insert(index, value); end
       def empty?; end
     end
   end
   

   Can also be written as follows.

   class AbstractList
     extend Abstractable
   
     abstract { def add(value); end }
     abstract { def insert(index, value); end }
     abstract { def empty?; end }
   end
   

Get defined abstract methods

abstract_methods returns an array containing the names of abstract methods in the receiver.
if set true to args include ancestors abstract methods (default true).

class AbstractDriver
  extend Abstractable
  abstract :open, :close
end

class AbstractIODriver < AbstractDriver
  abstract :read, :write
end

AbstractIODriver.abstract_methods # => [:read, :write, :open, :close]

If specify false for the argument, only abstract methods defined in the receiver is returned.

AbstractIODriver.abstract_methods(false) # => [:read, :write]

Undefine of abstract method

Can undefine and if you call Module#undef_method.
However, the receiver must be a class that defines an abstract method.
(Can't be undefine of the abstract methods of the parent class from a subclass.)

class Parent
  extend Abstractable
  abstract :greet
end

class Child < Parent
  undef_method :greet
end

begin
  Child.new # => NotImplementedError
rescue NotImplementedError
end

class Parent
  undef_method :greet
end

Child.new # => OK

Validation of unimplemented abstract method do always called?

Once you have confirmed that the unimplemented methods do not exist, validation does not take place.
if defined abstract method later, then perform validation once more.
required_validate? returns true if required unimplemented abstract methods validation.

class AbstractParent
  extend Abstractable
  abstract :greet
end

class Child < AbstractParent
  def greet; end
end

Child.required_validate? # => true
Child.new
Child.required_validate? # => false

# define abstract method
AbstractParent.abstract :execute

Child.required_validate? # => true

If define environment variable ABSTRACTABLE_IGNORE_VALIDATE

This case is required_validate? returns true always.
ABSTRACTABLE_IGNORE_VALIDATE value allow any value.

# Linux
export ABSTRACTABLE_IGNORE_VALIDATE=true
# windows
set ABSTRACTABLE_IGNORE_VALIDATE=true

Abstract method of singleton class

Abstract method of singleton class can't validation at new.
Therefore throw error at abstract method call.
But can find unimplemented abstract methods.

class AbstractParent
  class << self
    extend Abstractable
    abstract :greet
  end
end

class Child < AbstractParent
end

Child.greet # => greet is abstract method defined in
            # #<Class:AbstractParent>, and must implement.
            # (NotImplementedError)

Do explicitly validation

if call validate_not_implemented_abstract_methods then can do explicitly validation.

class AbstractParent
  extend Abstractable
  abstract :greet
end

class Child < AbstractParent; end

# explicitly validation
Child.validate_not_implemented_abstract_methods
# => following abstract methods are not implemented. (NotImplementedError)
#    [:greet] defined in AbstractParent

Find unimplemented abstract methods

abstractable#find_not_implemented_info returns a following format Hash

{abstract_class => array of unimplemented abstract methods, ...}

class AbstractParent
  extend Abstractable
  abstract :greet
end

class Child < AbstractParent; end

Abstractable.find_not_implemented_info(Child) # => {AbstractParent=>[:greet]}

If call find_not_implemented_info_from_singleton,
Then can find unimplemented abstract methods of singleton class.

class AbstractParent
  class << self
    extend Abstractable
    abstract :greet
  end
end

class Child < AbstractParent; end

Abstractable.find_not_implemented_info_from_singleton(Child)
# => {#<Class:AbstractParent>=>[:greet]}