I think your original example is UB. Enums are just like ints with named
values so doing `int x; std::cout << x;` is UB. You need at least `TestEnum
h{}` to have 0. Actually, allowing default values can break existing code
because right now `Enum e{};` always means e = 0, after your change the
value will be different.

On Fri, Mar 24, 2023 at 4:32 PM Aleksej Penkov via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> Dear team,
>
>
>
> I have a proposal to introduce an optional default-initializer for enum
> types.
>
> For me it looks like currently an enum variable is by default initialized
> with a default value of the underlying type.
>
>
>
> Code example:
>
> *#include <iostream>*
>
>
>
> *enum TestEnum {*
>
> * good = -100,*
>
> * bad = 200*
>
> *};*
>
>
>
> *int main()*
>
> *{*
>
> * TestEnum h;*
>
> * std::cout << h << std::endl;*
>
> * return 0;*
>
> *}*
>
>
>
> Output: *0*
>
>
>
> The resulting value 0 is neither of the range ones.
>
> The proposal is to have a way to specify the default one.
>
>
>
> See the possible example below:
>
> *#include <iostream>*
>
>
>
> *enum TestEnum {*
>
> * good = -100,*
>
> * bad = 200*
>
> *default:*
>
> * bad*
>
> *};*
>
>
>
> *int main()*
>
> *{*
>
> * TestEnum h;*
>
> * std::cout << h << std::endl;*
>
> * return 0;*
>
> *}*
>
>
>
> Output: *200*
>
>
>
> Why I brought this up.
>
> I've seen lots of code using kind of an enum below:
>
> *enum SomeEnum {*
>
> * Good = 0,*
>
> * SomeOption1,*
>
> * // some other values ...*
>
> * SomeOptionN,*
>
> * Invalid*
>
> *};*
>
>
>
> Any class/struct having this enum as a member could potentially initialize
> it by default to Good leading to a customer of this thinking the object is
> in a 'Good' shape althought it's just in some 'default' one.
>
> Changing that to:
>
> *enum SomeEnum {*
>
> * Good,*
>
> * SomeOption1,*
>
> * // some other values ...*
>
> * SomeOptionN,*
>
> * Invalid*
>
> *default:*
>
> * Invalid*
>
> *};*
>
> could prevent errors of using non-initialized objects.
>
>
>
> Having the 'default' initializer could decrease a number of errors with
> incomplete/improper initialization.
>
> Please let me know if this makes sense to your opinion.
>
>
>
> Kind regards,
>
> Aleksej Penkov
>
>
>
> *BMW Group*
>
> Aleksej Penkov
>
> BMW Car IT
>
> JC-6
>
> Senior Software Engineer
>
> Lise-Meitner-Straße 14
>
> 89081 Ulm
>
>
>
> Telephone: +4973137804118
>
> Mobile: +491742685058
>
> Mail: aleksej.penkov_at_[hidden]
>
> Web: https://www.bmw-carit.de
>
>
>
> -------------------------------------------------------------------------
>
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>
> Management: Chris Brandt and Michael Böttrich
>
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>
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>
>
>
>
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-- 
Regards,
Oleksandr Koval.