Saturday, July 21, 2012

c++ compilation dependency - my take on effC++

(Based on P144 effC++)

* size of each class instance
* #include
* header (assuming one header file per class) contains field listing of the class

These are the key points of ComplDependency. CD means that if an upstream file changes, then a downstream file needs recompiling.

As an analogy, imagine the "downstream" file (your app class) has an auto-generated Table of Contents of a large MS-word document. The Word document includes sub-documents (utility classes), which in turn include other sub-documents (lib classes). Edits in any included documents could render the TOC obsolete, and needs a re-compilation.

In the traditional (simple) design, the app class Person has its fields declared as type String, Date, Address etc. Any change in the size of Type Address triggers re-compilation of our class.

In pimpl or the java world, all those fields are moved into a PersonImpl class which is still CD on Type Address. However, the domino effect stops at PersonImpl. Our app class Person needs no recompilation since size of Type Person is unaffected.

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