I'm seeing an error related to templates (compiler is Visual Studio 2012) that I don't understand. Here's the code, boiled down to the essentials:
// Templated class - generic
template <typename T>
class Test
{
public:
void WorksFine() {} // Comiples and works as expected at runtime
void Problem();
};
// Templated class - expicit specialization for T = int.
template <>
class Test<int>
{
public:
void WorksFine() {} // Comiples and works as expected at runtime
void Problem();
};
// The definition below compiles and works fine at runtime.
template<typename T> void Test<T>::Problem() {}
// The definition below gives error C2910.
template<> void Test<int>::Problem() {printf("In Test::Problem(int instantiation)\n");}
For the WorksFine method, the function definition is inside the explicitly specialized class definition, and everything is fine. But for the Problem method, when I define the method outside the explicitly specialized class definition, I get error C2910
Why is this? Error C2910 indicates that the problem is that Test::Problem() is already defined. But it is not defined inside the class...there is no function definition only a declaration.
It seems pretty lame to be able to do something or not depending on where you choose to put the function definition, which I always though was more of a style/syntax decision, not a functionality/semantics decision. Am I missing something?
You don't need the template<>
. Just write:
void Test<int>::Problem() {printf("In Test::Problem(int instantiation)\n");}
The template<>
syntax on a member specialization is required where explicitly instantiating a member on its own ; it is omitted when defining a member of an already existing specialization.
template<typename T> struct X { static int i; };
template<> int X<int>::i = 0; // member instantiation, uses template<>
template<typename T> struct Y { static int i; };
template<> struct Y<int> { static int i; } // template specialization
int Y<int>::i = 0; // no template<>
You don't need template
anymore in the explicit function definition: void Test<int>::Problem() {printf("In Test::Problem(int instantiation)\\n");}
In this case g++ gives a slightly better error message error: template-id 'Problem<>' for 'void Test<int>::Problem()' does not match any template declaration
Try this:
// The definition below gives error C2910.
void Test<int>::Problem()
{
printf("In Test::Problem(int instantiation)\n");
}
int main()
{
Test<int> hey;
hey.Problem();
return 0;
};
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