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I scoured the C++11 standard (well, the n3242 draft) and the internet but could not find a precise answer. The code below compiles fine with clang 3.2 and g++ 4.7.2 as well as Visual Studio 2010, but I would expect to get an error instead. #include <iostream> #include <typeinfo> typedef int a_t; namespace a_ns { class a_t {}; } using a_ns::a_t; int main() { a_t a; std::cout << typeid(a).name() << std::endl; return 0; } Built with: clang -std=c++11 -pedantic -Wall -o a a.cpp -lstdc++ g++ -std=c++11 -pedantic -Wall -o a a.cpp -lstdc++ cl -EHsc -GR a.cpp clang and g++ generated executables print "i", which seems to indicate that the a is of type int and the typedef prevailed. cl generated executable prints "class a_ns::a_t" which seems to indicate that Visual Studio liked the using declaration more. I would expect the code not to compile according to the following standard excerpts. I would expect an error similar to "target of using declaration conflicts with declaration already in scope". 7.1.3.6 Similarly, in a given scope, a class or enumeration shall not be declared with the same name as a typedef-name that is declared in that scope and refers to a type other than the class or enumeration itself. 7.3.3.1 A using-declaration introduces a name into the declarative region in which the using-declaration appears. 7.3.3.2 Every using-declaration is a declaration [...] There's probably something I am missing in the standard that explains this behavior (or I am just too tired to see the obvious), but I cannot seem to find it. Thank you.

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