C++ Truths

The objective is to allow the following to be valid C++. #include <functional> struct Test { void func(int) {} }; void test() { std::function deduced = &Test::func; // compiler error std::function<void (Test *, int)> ex = &Test::func; // OK } With class template argument deduction in C++17, type arguments for std::function above should have been deduced. The first line in function test fails to compile as of this writing because std::function does not appear to have deduction guides for conversion from pointer to member functions. On the other hand, explicitly specifying the template arguments makes the compiler happy. The following deduction guide seems to fix the issue. namespace std { // warning: undefined behavior template<class R, class C, class... ArgTypes> function(R(C::*)(ArgTypes...)) -> function<R(C*, ArgTypes...)>; } void test() { std::function deduced = &Test::func; // Now, OK std::function<void (Test *,...