The code below is compiled successfully with both GCC and MSVC:
#include <iostream>
#include <sstream>
template <class C>
class basic_format
{
public:
template <typename T>
basic_format & operator << (const T & val)
{
out << val;
return *this;
}
std::basic_string<C> str() const { return out.str(); }
operator std::basic_string<C>() const { return str(); }
private:
std::basic_ostringstream<C> out;
};
using aformat = basic_format<char>;
using wformat = basic_format<wchar_t>;
class A {};
template <class C>
std::basic_ostream<C>& operator << (std::basic_ostream<C>& out, const A&)
{
return out << static_cast<C>('A');
}
int main()
{
A a;
const std::string val = aformat() << a;
std::cout << val << std::endl;
return 0;
}
Compiling with GCC:
g++ -std=c++20 -pthread a.cpp -o a
Compiling with MSVC:
cl /std:c++20 /EHsc a.cpp
