SubclassMustImplement

There are circumstances when it is desirable to specify certain methods as abstract, i.e. it is the responsibility of any subclass to implement them. Getting a MethodMIssing is not helpful; an error that explicitly explains that the missing method is required by contract will save much time.

Installation

Add this line to your application's Gemfile:

gem 'subclass_must_implement'

And then execute:

$ bundle

Or install yourself as:

$ gem install subclass_must_implement

Usage

Either include SubclassMustImplement or extend SubclassMustImplement in your base class. Then call subclass_must_implement with a list of required method names as symbols. You can optionally pass in a custom error message using the err_message named argument.

Example 1:

class BaseFoo
  include SubclassMustImplement

  subclass_must_implement :foo, :bar, :baz
end

class Foo < BaseFoo
  def foo
    :foo
  end
end

f = Foo.new
f.foo # returns :foo
f.bar # raises a NotImplementedError that "bar" must be implemented in the subclass
f.baz # raises a NotImplementedError that "baz" must be implemented in the subclass
f.qux # raises a MethodMissing

Example 2:

class BaseBar
  extend SubclassMustImplement

  subclass_must_implement :foo, :bar, err_message: "Version expected!!!"
end

class Bar < BaseBar
  def bar
    :bar
  end
end

b = Bar.new
b.bar # return :bar
b.foo # raises a NotImplementedError with the specified error message "Version expected!!!"

Contributing

1. Fork it ( https://github.com/[my-github-username]/subclass_must_implement/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request
6. Make sure all the test pass and your changes have test coverage!