Code generators provide added complexity to a build system. From the start, VTK provided a system that automatically wrapped the C++ code into Tcl, Python, and Java by parsing the C++ header files, and automatically generating a wrapping layer. This requires a build system that can build a C/C++ executable (the wrapper generator), then run that executable at build time to create more C/C++ source code (the wrappers for the particular modules). That generated source code must then be compiled into executables or shared libraries. All of this has to happen within the IDE environments and the generated Makefiles.