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Fozefy
Fozefy

Reputation: 685

Enum class operator override

I have an enum class defined like so in myClass.h:

enum class SpeedMode {
  SPEED_SLOW = 0,
  SPEED_NORMAL = 1,
  SPEED_FAST = 2
};

In another file I'd like to use my enum as an int:

void myOtherClass::myFunc(const SpeedMode& speed_mode) {
  int speed_as_int = speed_mode;
.
.
.
}

In the same file I defined my enum (myClass.h) I try to define an operator override:

int operator= (const SpeedMode& mode) {
   return static_cast<int>(mode); //The real logic is more complex and will use a switch statement
}

But I get this error: error: 'int operator=(const SpeedMode&)' must be a nonstatic member function.

If I try to wrap it in something like struct SpeedModeUtils { } which allows that file to compile but then myOtherClass gives me this error where I try to make use of the override: error: cannot convert 'const SpeedMode' to 'int' in initialization

I'm aware I could use the old non-class enum, but this is a large project and I much prefer the type safety of an enum class. I'm also aware I can use static_cast but I'd prefer to avoid that for likely obvious reasons.

If this fails I'll simply use a manual conversion function, but figured this would be a 'nicer' way of handling this.

Upvotes: 0

Views: 823

Answers (2)

Lars Kakavandi-Nielsen
Lars Kakavandi-Nielsen

Reputation: 2198

You need access to the underlying data type of the enum class, meaning the int. The way to do this is to use std::underlying_type<T> to access the integer value. The way you do this is:

#include <type_traits>

auto speed_mode_as_int = static_cast<std::_underlying_type<SpeedMode>::type>(speed_mode);

I made a minimum working example here which should get you started

#include <type_traits>
#include <iostream>
#include <cassert>

enum class SpeedMode {
    SPEED_SLOW = 0,
    SPEED_NORMAL = 1,
    SPEED_FAST = 2
    
};

bool is_fast(const SpeedMode& speed_mode)
{
    auto speed_mode_as_int =
        static_cast<std::underlying_type<SpeedMode>::type>(speed_mode);

    switch(speed_mode_as_int)
    {
    case 2:
        return true;
    default:
        return false;
    }
}
    

int main(void) {

    auto mode = SpeedMode::SPEED_SLOW;

    assert(false == is_fast(mode));
    mode = SpeedMode::SPEED_NORMAL;
    assert(false == is_fast(mode));
    mode = SpeedMode::SPEED_FAST;
    assert(true == is_fast(mode));
        
    return 0; 
}

I compiled it with the following compile string: clang++ -std=c++17 main.cpp.

Upvotes: 1

Gustaw
Gustaw

Reputation: 19

As a compiler said you, you can't define such an assignment operator. It said int operator=(const SpeedMode&)' must be a nonstatic member function, enums just do not have members in C++.

Upvotes: 0

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