7.4.4 Sharing Template Repositories

Templates that are within a repository must not violate the one-definition rule of the ISO C++ standard. That is, a template must have the same source in all uses of the template. Violating this rule produces undefined behavior.

The simplest, though most conservative, way to ensure that the rule is not violated is to build only one program or library within any one directory. Two unrelated programs might use the same type name or external name to mean different things. If the programs share a template repository, template definitions could conflict, thus yielding unpredictable results.