Bad Smells: Library classes

A modern application will use library classes. Sometimes these put us in a dilemma. We want the bookstore to be different, but we don’t want to change it. Even when it is possible to change libraries, it carries risks: It affects other clients and this implies redoing our changes for future versions of the library.

Incomplete Library Class

Symptoms

You are using a library and there is a feature you would like it to have.

To do

• Contact the creator to see if they can incorporate the feature.
• If it’s just a couple of methods, use Enter Foreign Method in the library client class. This generates Feature Envy but it is insurmountable.
• If there are enough methods, use Introduce Local Extension (creating a subclass of the library to create new pseudo-libraries). Use the new extended class to advance.
• You can decide to introduce a layer to wrap the bookcase.

Rewards

Reduces duplication (when you can reuse library code instead of implementing it completely from scratch).

Contraindications

If several projects incorporate a library in incompatible ways, it may involve extra work to adapt to future changes to it.