10 Modules [module]

10.5 Private module fragment [module.private.frag]

module-keyword : private ; declaration-seq
A private-module-fragment shall appear only in a primary module interface unit ([module.unit]).
A module unit with a private-module-fragment shall be the only module unit of its module; no diagnostic is required.
[Note 1: 
A private-module-fragment ends the portion of the module interface unit that can affect the behavior of other translation units.
A private-module-fragment allows a module to be represented as a single translation unit without making all of the contents of the module reachable to importers.
The presence of a private-module-fragment affects:
— end note]
[Example 1: export module A; export inline void fn_e(); // error: exported inline function fn_e not defined // before private module fragment inline void fn_m(); // error: non-exported inline function fn_m not defined static void fn_s(); export struct X; export void g(X *x) { fn_s(); // OK, call to static function in same translation unit } export X *factory(); // OK module :private; struct X {}; // definition not reachable from importers of A X *factory() { return new X (); } void fn_e() {} void fn_m() {} void fn_s() {} — end example]