Overloading enum boolean comparison?

Question

I have a enum that I am trying to create operator overloads. I am struggling with the boolean comparison operator.

Here is what I have:

enum class TraceLevel : uint32_t {

    // Basic logging levels (may be combined with trace level)
    All = 0xFFFFFFFF,
    None = 0x00000000,
    Info = 0x00000001,
    Warning = 0x00000002,
    Error = 0x00000004,
    Logging = 0x0000000F,
};

inline bool operator&&(TraceLevel __x, TraceLevel __y) {
    return static_cast<uint32_t>(__x & __y) > 0;
}

inline constexpr TraceLevel
operator&(TraceLevel __x, TraceLevel __y) {
    return static_cast<TraceLevel>
        (static_cast<uint32_t>(__x) & static_cast<uint32_t>(__y));
}

So with this enum class, I can issue the statements:

LogLevel a = LogLevel::Info;
LogLevel b = LogLevel::Warning;

LogLevel c = a & b;

But I also want to do:

if( a && b) {
   //do work
}

My inline operator declaration for && is not correct, but I am not sure what to change it to.

Ideas?

Don't prefix your identifiers with underscores. It's reserved for the implementation. Also, what are the semantics you expect for your operator &&? Currently, it will only return true if both operands have at least one common bit set. Only you can tell whether this is what you want. — 5gon12eder
– 5gon12eder, Commented Feb 18, 2015 at 23:01

amdn · Accepted Answer · 2015-02-18 23:17:35Z

1

There's a couple of problems with your code

You define TraceLevel but use LogLevel
Your definition of operator& is after your use of it in the definition of operator&&

I have renamed LogLevel to be TraceLevel and have moved the definition of operator& to be before the definition of operator&& (and as suggested in the comment removed underscores), see working example here.

#include <iostream>

enum class TraceLevel : uint32_t {

    // Basic logging levels (may be combined with trace level)
    All = 0xFFFFFFFF,
    None = 0x00000000,
    Info = 0x00000001,
    Warning = 0x00000002,
    Error = 0x00000004,
    Logging = 0x0000000F,
};

inline constexpr TraceLevel
operator&(TraceLevel x, TraceLevel y) {
    return static_cast<TraceLevel>
        (static_cast<uint32_t>(x) & static_cast<uint32_t>(y));
}

inline bool operator&&(TraceLevel x, TraceLevel y) {
    return static_cast<uint32_t>(x & y) > 0;
}

int main() {

    TraceLevel a = TraceLevel::Info;
    TraceLevel b = TraceLevel::Warning;

    TraceLevel c = a & b;

    if( a && b) {
        std::cerr << "a && b is true\n";
    } else {
        std::cerr << "a && b is false\n";
    }
}

answered Feb 18, 2015 at 23:17

amdn

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2 Comments

user3072517 Over a year ago

On #1, yeah, that was a typo. I actually had it in my program as TraceLevel LogLevel = TraceLevel::Warning; Got them corn-fused when I retyped. As far as the order, ah, that makes sense. However, even changing the order VS2013 still chokes on it. I get these three errors when I try to put it in the way it works in Coliru: error C2146: syntax error : missing ';' before identifier 'TraceLevel', error C2433: 'constexpr' : 'inline' not permitted on data declarations and finally error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

user3072517 Over a year ago

Doh!! Nevermind...my bad. Thanks for the tip on the order!

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