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[std-proposals] Dispatching enum class

From: Gergely Nagy <gergely.nagy.alt_at_[hidden]>
Date: Fri, 1 Apr 2022 18:00:37 +0200

I have a wild idea, which might or might not be useful, just curious if
anyone likes it. Basically enum classes could be enhanced with a built in
way to dispatch function calls based on their value, they could even set
next value effectively implementing a state machine:

enum class DispatchStuff(int Arg1, double Arg2) : int {
     VALUE_1 {
       std::cout << "VALUE_1 int:" << Arg1 << " dbl:" << Arg2 << std::endl;
       *this = VALUE_2;

    VALUE_2 {
       std::cout << "VALUE_2 int:" << Arg1 << " dbl:" << Arg2 << std::endl;
       *this = VALUE_1;

    default {
        throw InvalidValueException();

And this could be used as:

int main() {
    DispatchStuff state{DispatchStuff::VALUE_1};

    state(1, 3.14);
    state(2, 10.0);

So it would be like a normal enum, but it would be callable, and had a
state. I know this can be done now, but the same can only be achieved by a
load of boilerplate, especially for large state enums.

I find it redundant to list the whole enum, then have a switch-case
function to handle the dispatching. And this is also error-prone, as with
new enum values the dispatch function also needs to be changed.

It might not worth it, just an idea.


Received on 2022-04-01 16:00:49