I'm not new to programming but i try to understand the concept of concepts in c++20 a little bit more in depth.
situation: I'm playing around with a method in a class like (content of my header file):
// in my mind: a concept testing if there is a typename matching with
// std::to_string(...)
template<typename T>
concept IsStringable = requires (T t) {
{ std::to_string(t) }; // NOTE: there must be a to_string overloaded version
// with type T
};
class example_class_with_concept_methode {
private:
// some unnecessary stuff
// implementation outsourced to cpp file
std::string _replacePlaceholder(std::string fmtMsg,
std::string reg,
std::string replacementMsg);
public:
// ctor & co.
std::string processMessage(std::string msg, IsStringable auto replaceMsgValue) {
std::string replaceMsg = std::to_string(replaceMsgValue);
return _replacePlaceholder(fmtMsg, _pattern, replaceMsg);
}; // class example_class_with_concept_methode
The CMakeLists.txt files are working with the above shown code (GCC 10.2.1 x86_64-linux-gnu, CMake 3.18.4). But target solution would be outsourcing the concept method also to the cpp file (what was done with all other class methods).
BUT (question): If I outsource this one method to cpp I'm getting multiple errors for undefined references for different versions the compiler would make out of the concept statement for replaceMsgValue. What am I doing wrong here?
Do I need to keep this implementation in header file or is there a way to outsource it to the cpp file?
