Modern C++ Programming Cookbook

How to do it...

To provide multiple versions of a library and let the user decide what version to use, do the following:

• Define the content of the library inside a namespace.
• Define each version of the library or parts of it inside an inner inline namespace.
• Use preprocessor macros and #if directives to enable a particular version of the library.

The following example shows a library that has two versions that clients can use:

    namespace modernlib     {       #ifndef LIB_VERSION_2       inline namespace version_1       {         template<typename T>         int test(T value) { return 1; }       }       #endif       #ifdef LIB_VERSION_2       inline namespace version_2       {         template<typename T>         int test(T value) { return 2; }       }       #endif     }