C++ remains one of the most widely used languages in various computing
fields, from embedded programming to high-performance computing. While
new features are constantly being added to C++, an important aspect of
the language that is often overlooked is its compilation time. Merely
including a few header files can cause compilation time to increase
significantly. An alternative to including header files is using
forward declarations; however, the rules for forward declaring classes
and functions are non obvious and confusing to most
developers. Additionally, forward declaring methods, as well as
functions that accept lambdas as arguments, is not possible. In this
paper, we present a novel technique, termed Header Substitution, to
automatically detect opportunities for forward declarations with the
goal of replacing includes of header files and improving compilation
time. Header Substitution also introduces function wrappers as an
alternative to forward declaring methods and functions with lambda
arguments. We implemented Header Substitution in a tool, dubbed Yalla,
and applied it to various C++ projects in order to speed up the
development cycle, i.e., the debugging, editing, compiling, and
rerunning loop, achieving up to a 24.5x speedup when compiling C++
files and a 4.68x speedup of the development cycle.