What are inline namespaces good for? -- StackOverflow
Quick A: For source-level library versioning.
A StackOverflow classic:
What are inline namespaces for?
C++11 allows
inline namespaces, all members of which are also automatically in the enclosing namespace. I cannot think of any useful application of this -- can somebody please give a brief, succinct example of a situation where aninline namespaceis needed and where it is the most idiomatic solution?(Also, it is not clear to me what happens when a
namespaceis declared inline in one but not all declarations, which may live in different files. Isn't this begging for trouble?)

While we're waiting for Concepts Lite, Eric shows how we can already do quite a bit in C++11 while planning for a transition to language support when it's available.