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#include <iostream> 
 
// in the normal case, just the identity
template<class T>
struct item_return{ typedef T type; };
 
template<class T>
typename item_return<T>::type foo(){ return T(); }
 
template<>
struct item_return<float>{ typedef int type; };
 
template<>
int foo<float>(){ return 42; }
 
// might want to stick to the following
// so you only need to update the return-type in one place
// namely, the `item_return` specialization
//template<>
//item_return<float>::type foo<float>(){ ... }
// note: No `typename` needed, because `float` is not a dependent type
 
int main(){
	std::cout << "out = " << foo();
}

prog.cpp: In function ‘int main()’:
prog.cpp:24:31: error: no matching function for call to ‘foo()’
  std::cout << "out = " << foo();
                               ^
prog.cpp:8:31: note: candidate: template<class T> typename item_return<T>::type foo()
 typename item_return<T>::type foo(){ return T(); }
                               ^~~
prog.cpp:8:31: note:   template argument deduction/substitution failed:
prog.cpp:24:31: note:   couldn't deduce template parameter ‘T’
  std::cout << "out = " << foo();
                               ^

Standard output is empty