Using inline namespaces for symbol versioning

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.

Getting ready

In this recipe, we will discuss namespaces and nested namespaces, templates and template specializations, and conditional compilation using preprocessor macros. Familiarity with these concepts is required in order to proceed with the recipe.

How to do it...

To provide multiple versions of a library and let the user decide what version...