The C++11 standard has introduced a new type of namespace called inline namespaces that are basically a mechanism that makes declarations from a nested namespace look and act like they were part of the surrounding namespace. Inline namespaces are declared using the inline keyword in the namespace declaration (unnamed namespaces can also be inlined). This is a helpful feature for library versioning, and in this recipe, we will see how inline namespaces can be used for versioning symbols. From this recipe, you will learn how to version your source code using inline namespaces and conditional compilation.