Can do you something with “using enum” support in C++20 to bring the enum
into the same namespace as the function?

Sincerely,
   Alan


On Wed, Mar 12, 2025 at 4:08 PM Jeremy Rifkin via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> > It would looks like a mess:
>
> Not really. You're free to format your code as a mess or not, simply
> putting enum constants and member functions together separated by a newline
> would be plenty clean.
>
> > Or just allow to assign a function to a value.
> > Second solution for me looks better.
>
> Except it would be very confusing. You want to use the same syntax as enum
> constants, but not for an enum constant.
>
> Cheers,
> Jeremy
>
> On Wed, Mar 12, 2025 at 5:46 PM Dmitrii Shabalin via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
>
>> Hi Tom.
>>
>> enum class E {
>> A, B, C
>> std::string_view to_string(E value) { … }
>> }
>>
>> It would looks like a mess:
>>
>> enum class E {
>> A = 1, B, C = 3
>> std::string_view to_string(E value) { … }
>> D = A, E = calcE("E"), F
>> E from_string(std::string value) { … }
>> G, H, max = H
>> bool IsValueExists(E Value)
>> }
>>
>> So, you need a clear keyword to separate enumeration from functions. Or
>> just allow to assign a function to a value.
>> Second solution for me looks better.
>>
>> Kind regards,
>> Dmitrii shabalin
>>
>>
>>
>> чт, 13 мар. 2025 г. в 06:04, Tom Honermann via Std-Proposals <
>> std-proposals_at_[hidden]>:
>>
>>> On 3/11/25 10:23 PM, Jeremy Rifkin via Std-Proposals 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.
>>>
>>> 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_at_[hidden]> 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_at_[hidden]>:
>>>>
>>>>> 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_at_[hidden]> 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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