Similar to this question about explicit specialisation of static const class members of a template class, and this question about explicit specialisation of a template class, but my issue is with explicit specialisation of a variable template.
My MCVE:
//my_templated_literal.h
#pragma once
template <typename T>
constexpr T val;
//my_specialised_literal.h
#pragma once
#include "my_templated_literal.h"
template <>
constexpr int val<int> = 2;
//my_specialised_literal.cc
#include "my_specialised_literal.h"
//main.cc
#include "my_specialised_literal.h"
int main() {}
Compile command: $CXX -std=c++14 my_specialised_literal.cc main.cc
This compiles and seems to work as expected on just about every compiler version I've tried, but gives linker errors with clang-9:
/tmp/main-ec49c7.o:(.rodata+0x0): multiple definition of `val'
/tmp/my_specialised_literal-521691.o:(.rodata+0x0): first defined here
Is this an ODR violation silently accepted by most compiler versions, or is clang-9 wrong in some way? If the former, I know that if I could use C++17 I could fix it by making the specialisation inline, but what is a C++14 fix for the problem?