sfinae0.cpp:15:5: error: call to 'doSomething' is ambiguous
    doSomething( a );
    ^~~~~~~~~~~
sfinae0.cpp:3:6: note: candidate function [with T = A]
auto doSomething( T &t ) -> decltype( t.doSomething() ) {
     ^
sfinae0.cpp:7:5: note: candidate function [with T = A]
int doSomething( T &t ) {
    ^
1 error generated.