Sunday, January 9, 2022

[SOLVED] C2244: 'MyTemplateClass<T>::MyFunction': unable to match function definition to an existing declaration

Issue

Could someone explain why the following code compiles on GCC, but not in Visual Studio.

I get error C2244: 'MyTemplate::List': unable to match function definition to an existing declaration at the noted line.

#include <array>

enum class MyEnum
{
    MAX = 5,
};

template<typename E> 
class MyTemplate
{
public :
    static const int NUMBER = static_cast<int>(E::MAX);
    std::array<int, NUMBER> List(); 
};

template<typename E>
std::array<int, MyTemplate<E>::NUMBER> MyTemplate<E>::List() // ERROR
{
    return std::array<int, MyTemplate<E>::NUMBER>();
}

int main()
{
    MyTemplate<MyEnum> myClass;
}

I presume it's something non-standard I'm doing that GCC allows and VS doesn't, but I can't figure out what. CLion is also happy with the code.

Given this answer it's also possible it's a bug in VS, although the specifics are different, the error message is the same. In my case the template seems simple however, involving one parameter and no nesting.


Solution

As workaround, you might use:

template<typename E>
auto MyTemplate<E>::List()
-> std::array<int, NUMBER>
{
    return std::array<int, MyTemplate<E>::NUMBER>();
}

Demo



Answered By - Jarod42
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