Partitioning your project
As our solutions grow in the number of lines and files they have, we slowly understand that the inevitable is coming: either we start partitioning the project or we drown in lines of code and a multitude of files. We can approach this problem in two ways: by portioning the CMake code and by moving the source files to subdirectories. In both cases, we aim to follow the design principle called separation of concerns. Put simply, break your code into chunks, grouping code with closely related functionality while decoupling other pieces of code to create strong boundaries.
We talked a bit about partitioning CMake code when discussing listfiles in Chapter 1, First Steps with CMake. We spoke about the include() command, which allows CMake to execute the code from an external file. Calling include() doesn't introduce any scopes or isolations that are not defined within the file (if the included file contains functions, their scope will be handled correctly...
