Tuesday coding tips are super short posts about various tidbits mainly from C++, but also from other programming languages I use. You can also follow the #TuesdayCodingTips hashtag on Mastodon and Linkedin.
Suppose you have a C++ function for opening a file stream that accepts a path to a file and a string (view) with open-mode specifications (like fopen). The issue is, even though your API is strongly typed, users can still swap the arguments by accident and don’t get a compile time error, due to implicit conversions from string-like constants.
Luckily, there is an easy hack with which you can disable implicit conversions for one particular function by explicitly deleting all overloads (via auto template) and allowing just one particular version. The coolest thing is that even the return value doesn’t have to match!
#include <filesystem>
using path = std::filesystem::path;
void fopen2(const auto&, const auto&) = delete;
FILE* fopen2(const path& fp, const std::string& mode)
{
/* dummy implementation */
return nullptr;
}
int main()
{
// error: call to deleted function 'fopen2'
// note: candidate function [with auto:1 = char[11], auto:2 = char[2]] has been explicitly deleted
fopen2("myfile.txt", "r");
// This is ok
fopen2(path { "myfile.txt" }, std::string { "r" });
return 0;
}