Is there a better way to express nested namespaces in C++ within the header

To avoid really deep indenting, I usually do it this way:

namespace A { namespace B { namespace C
{
    class X
    {
        // ...
    };
}}}

C++17 might simplify nested namespace definition:

namespace A::B::C {
}

is equivalent to

namespace A { namespace B { namespace C {
} } }

See (8) on namespace page on cppreference:
http://en.cppreference.com/w/cpp/language/namespace

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