The Benefits of Composite Refactorings
The composite refactorings in this book, each of which targets a particular pattern, have some of the following benefits.
They describe an overall plan for a refactoring sequence.
The mechanics of a composite refactoring describe the sequence of low-level refactorings you can apply to improve a design in a particular way. Do you need such a sequence? If you already know the low-level refactorings, you can certainly apply them in whatever order you see fit.
However, the refactoring sequences in this catalog may prove to be more safe, effective, or efficient in improving your design than your own refactoring sequences are. I once followed certain low-level refactorings to refactor to the State [DP] pattern. Then I learned a better, safer sequence. Then someone suggested improvements to that sequence. By the time I got to the fifth version of the sequence, I knew I had a much better way of refactoring to the State pattern, and it was far different from my initial approach.
They suggest nonobvious design directions.
Composite refactorings begin at a source and take you to a destination. The destination may or may not be obvious, given your source. Much depends on your familiarity with patterns, each of which defines a destination as well as the forces that suggest the need to go towards or to that destination. The composite refactorings in this book make these nonobvious design directions clearer by describing real-world cases in which it made sense to move in the direction of a pattern.
They provide insights into implementing patterns.
Because there is no right way to implement a pattern (see There Are Many Ways to Implement a Pattern, 26), it's useful to consider alternative pattern implementations. This is particularly true of patterns that solve different kinds of design problems. For example, this book contains three different refactorings to Composite [DP] and three different ways to refactor to Visitor [DP]. How you refactor to these patterns and others will vary depending on the initial problem you face. In recognition of that, the refactoring sequences in this book vary in how they ultimately implement a pattern.