Use include-what-you-use to trim down included header files

include-what-you-use is a great tool that can be used to trim down the header files that we include in every file.

"Include what you use" means this: for every symbol (type, function variable, or macro) that you use in foo.cc, either foo.cc or foo.h should #include a .h file that exports the declaration of that symbol. The include-what-you-use tool is a program that can be built with the clang libraries in order to analyze #includes of source files to find include-what-you-use violations, and suggest fixes for them.

The main goal of include-what-you-use is to remove superfluous #includes. It does this both by figuring out what #includes are not actually needed for this file (for both .cc and .h files), and replacing #includes with forward-declares when possible.

Why this is useful?

Excerpt from Why Include What You Use?

• Faster Compiles
• Fewer Recompiles
• Allow Refactoring
• Self-documentation
• Dependency Cutting