template<typename T> int globalVar = 123; This is a variable template; globalVar<double> var; You have kind of 3 types here, not 2: globalVar<double>, double and int As far as I understand, you want to extract the template parameter double from globalVar<double>, before it is resolved. But you also want to get it from wherever it is used with auto: auto var = globalVar<double>; In this case, you want to get double from var.