Overloaded Function as Argument to Templated Function

June 28, 2023

I have stumbled upon an issue with templates in clang++ that I do not know how to solve.

I wish to use templated functions that take a class and a function as arguments. But when the function is an overloaded function, I get the error candidate template ignored: couldn't infer template argument 'F' which is totally sensible.

For instance, the example program

#include <iostream>
#include <math.h>

template<class T, typename F>
T foo(F f,T x){
  return f(x);
}

int main(void) {
  std::cout << "foo(sinf,0.34) is " << foo(sinf,0.34) << std::endl;
  return 0;
}

works exactly as I want. Now, if I use an overloaded function such as sin instead of sinf, the template argument cannot be inferred. How can I change the function template of foo to help the compiler resolving the type of F?

>Solution :

You can use a lambda to solve the ambiguity with overloads, eg:

foo([](double d){ return sin(d); }, 0.34)

On a side note, in C++, you should use <cmath> instead of <math.h> directly. You can use using namespace std; or better using std::sin; to bring std::sin into the calling namespace if you don’t want to qualify it at the call site.