dependency

Attribute with null object default

Examples

A Weak Null Object

Responds to any method

class Example
  dependency :some_attr
end

e = Example.new
e.some_attr.anything # => No error raised

A Strict Null Object

Responds only to the methods of the provided class

class SomeDependency
  def some_method
    # ...
  end
end

class Example
  dependency :some_attr, SomeDependency
end

e = Example.new
e.some_attr.some_method # => No error raised
e.some_attr.anything # => NoMethodError is raised

Specialized Substitute

If the class used to define the null object's strict interface has an inner Substitute namespace that has a build method, the null object will be the object returned from that build method.

class SomeDependency
  def some_method
    # ...
  end

  module Substitute
    def self.build
      SomeOtherNullObjectLibrary.etc
    end
  end
end

class Example
  dependency :some_attr, SomeDependency
end

e = Example.new

Activation

The Dependency module must be included in a class that will use the dependency macro.

However, the Dependency module can be included anywhere within the object hierarchy by using the Dependency.activate method.

class Example
end

Dependency.activate Example

class Example
  dependency :some_attr
end

As in the example above, for a class to be "activated" for Dependency, it must have already been defined. The dependency class method must be visible to the class using it, either my including it in the class directly, or by including it in any super class of the using class.

If no class is specified, Dependency is included in Object, making the dependency macro available in all Ruby classes.

Dependency.activate

class Example
  dependency :some_attr
end

License

The dependency library is released under the MIT License.