Hi,

> Sorry, Jeremy, but there is no straight way to add a normal function into enum.

The problem is: enum is enumeration. If you stop enumeration for a function, it would break the logic of the enum.

An implementation developer can weight in about challenge with adding this to existing implementations but there is no reason C++ cannot support this. To elaborate on what I mean, imagine syntax along the following lines:

enum class E {

  A, B, C

  std::string_view to_string(E value) { … }

}

E e = E::A;

e.to_string();

I would use deducing this to support member function call syntax.

enum class E {
  A, B, C;
  std::string_view to_string(this E value) { … }
};
E e = E::A;
auto name = e.to_string();

Tom.

Cheers,

Jeremy

On Tue, Mar 11, 2025 at 20:23 Dmitrii Shabalin via Std-Proposals <std-proposals@lists.isocpp.org> wrote:

Hi.
Sorry, Jeremy, but there is no straight way to add a normal function into enum.

The problem is: enum is enumeration. If you stop enumeration for a function, it would break the logic of the enum.

For me, the only way is accepting a value as a function.

Actually, it might work too:

std::string ToString( Test test)  { if (value == testValue)  return "testValue"; else return ""; }

enum Test{

testValue = 0,

toString = ToString,

max = testValue

}

std::cout << "Test value" << Test::toString(Test::testValue);

but as you can see, it causes having a function in the different namespace.

If you have any idea how to have a function inside in the enum, please, share your idea with an example.

Kind regards,

Dmitrii shabalin

ср, 12 мар. 2025 г. в 12:32, Jeremy Rifkin via Std-Proposals <std-proposals@lists.isocpp.org>:

Hi,

It seems weird to add a special-case to just allow lambdas in enums like this. The syntax is confusing too, it resembles enum constant syntax and this isn't syntax that exists for other similar language constructs.

I would much rather see enums get normal member functions like most other languages have.

Cheers,

Jeremy

On Tue, Mar 11, 2025 at 6:20 PM Dmitrii Shabalin via Std-Proposals <std-proposals@lists.isocpp.org> wrote:

Hi.

Since C++11 we have lambdas.

I believe, everyone, who works with enums, write some functions for this particular enum only.

However, there is no way to associate this function with the enum's namespace.

My idea: we can set a value for any of enum fields. It should be const and could be constexpr.

May be, we can set a lambda for a field too?

something like:

enum Test{

testValue = 0,

toString =[](Test value) -> std::string { if (value == testValue)  return "testValue"; else return ""; },

max = testValue

}

And usage will be something like:
std::cout << "Test value" << Test::toString(Test::testValue);

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