The following code compiles with gcc and clang (and many other C++11 compilers)
#include <stdint.h>
typedef int datatype;
template <typename T>
struct to_datatype {};
template <>
struct to_datatype<int16_t> {
static constexpr datatype value = 1;
};
template <typename T>
class data {
public:
data(datatype dt = to_datatype<T>::value) {}
};
int main() {
data<char> d{to_datatype<int16_t>::value};
}
when compile with (almost) latest MSVC
> cl .\test.cpp /std:c++latest /permissive-
Microsoft (R) C/C++ Optimizing Compiler Version 19.24.28314 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
test.cpp
.\test.cpp(16): error C2039: 'value': is not a member of 'to_datatype<T>'
with
[
T=char
]
.\test.cpp(16): note: see declaration of 'to_datatype<T>'
with
[
T=char
]
.\test.cpp(20): note: see reference to class template instantiation 'data<char>' being compiled
Is this a bug of MSVC? If yes, which term in C++ standard best describe it?
If you replace part of the code with
template <typename T>
class data {
public:
data(datatype dt) {}
data() : data(to_datatype<T>::value) {}
};
it compiles smoothly anyway.
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