Practical OOD in Ruby : Addison - Wesley

poodr - ch 3

Recognize Dependency : 
	-> A class has another class
	-> calls method in another class
	-> Args that message(method) requires. Gear knows Wheel.new 
requires rim and tire as well as order of Args.

More coupling -> More dependency
Tightly coupled two objects act as single entity
Avoid message chaining on different objects
If you cannot remove dependency from class just isolate them.

Use wrapping method to isolate external dependency.

Dependency have direction : By reversing direction of dependency code can be optimized.

_________________________________________________
|    Abstract Zone     |      Danger Zone       |    /|\  Dependency More
|______________________|________________________|     |
|    Neutral Zone      |      Neutral Zone      |     |
|______________________|________________________|     |   Dependency Less

Change less                            Change more
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