I am facing the following problem. Supposing I have two (or more) enum classes like these:
enum class CURSOR { ON, OFF };
enum class ANSI { ON, OFF };
I am trying to implement a (template) function called OPTION
able to do something like this:
OPTION( CURSOR::ON );
OPTION( ANSI::ON );
I tried implementing it in this way:
template <typename T>
inline void OPTION( const T& opt )
{
if( opt == CURSOR::ON ) //do something...;
else if( opt == CURSOR::OFF ) //do something...;
else if( opt == ANSI::ON ) //do something...;
else if( opt == ANSI::OFF ) //do something...;
}
But it gives me the following error if I try to compile the two previously defined lines of code:
examples/../include/manipulators/csmanip.hpp: In instantiation of 'void osm::OPTION(const T&) [with T = CURSOR]':
examples/manipulators.cpp:190:14: required from here
examples/../include/manipulators/csmanip.hpp:88:18: error: no match for 'operator==' (operand types are 'const osm::CURSOR' and 'osm::ANSI')
88 | else if( opt == ANSI::ON ) enableANSI();
| ~~~~^~~~~~~~~~~
examples/../include/manipulators/csmanip.hpp:88:18: note: candidate: 'operator==(osm::ANSI, osm::ANSI)' (built-in)
examples/../include/manipulators/csmanip.hpp:88:18: note: no known conversion for argument 1 from 'const osm::CURSOR' to 'osm::ANSI'
examples/../include/manipulators/csmanip.hpp:88:18: note: candidate: 'operator==(osm::CURSOR, osm::CURSOR)' (built-in)
examples/../include/manipulators/csmanip.hpp:88:18: note: no known conversion for argument 2 from 'osm::ANSI' to 'osm::CURSOR'
examples/../include/manipulators/csmanip.hpp:89:18: error: no match for 'operator==' (operand types are 'const osm::CURSOR' and 'osm::ANSI')
89 | else if( opt == ANSI::OFF ) disableANSI();
Please ignore the fact that I defined them in a namespace osm
in my code.
Do you know what is the problem and if you know how to build a function which works for this task? Thanks.
CodePudding user response:
One option would be to write several overloaded functions, each of which handles a different enumerated type. For example:
void OPTION(CURSOR c) {
switch (c) {
case CURSOR::ON: /* turn cursor on */; break;
case CURSOR::OFF: /* turn cursor off */; break;
}
}
void OPTION(ANSI a) {
switch (a) {
case ANSI::ON: /* turn ANSI on */; break;
case ANSI::OFF: /* turn ANSI off */; break;
}
}
Overload resolution will then pick the right function to call:
OPTION(CURSOR::OFF); // Calls first function
OPTION(ANSI::ON); // Calls second function
CodePudding user response:
I agree with 273K and templatetypedef about using overloads instead.
However, if you have your heart set on having a template with the case handling logic all in one place, you can do it this way:
#include <iostream>
#include <type_traits>
using std::cout;
enum class CURSOR { ON, OFF };
enum class ANSI { ON, OFF };
template <typename T>
void OPTION(T opt) {
if constexpr (std::is_same_v<T, CURSOR>) {
if (opt == CURSOR::ON) cout << "cursor is on\n";
else if (opt == CURSOR::OFF) cout << "cursor is off\n";
} else if constexpr (std::is_same_v<T, ANSI>) {
if (opt == ANSI::ON) cout << "ANSI is on\n";
else if (opt == ANSI::OFF) cout << "ANSI is off\n";
}
}
int main() {
OPTION( CURSOR::ON );
OPTION( ANSI::ON );
}