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Subject: Re: [std-proposals] explicit class
From: Magnus Fromreide (magfr_at_[hidden])
Date: 2019-11-13 02:39:56


On Mon, Nov 11, 2019 at 11:47:18AM -0700, Steve Weinrich via Std-Proposals wrote:
> This is an idea that has been roaming around my head for some 20 years!
>
>
>
> As we know, there is a list of some 15 (or so) operations (construction,
> assignment, copy, move, conversion, etc.) that the simple statement: "class
> T {};" defines.
>
>
>
> If one wishes some control over this behavior, one has to be knowledgeable
> in all that the compiler provides. In non-C++ terms, one has to say (modern
> use: =delete), "I don't want that, I don't want this, etc." The compiler
> provides no aid for this!
>
>
>
> My notion is to reverse this via "explicit class T {};". While I am sure
> there are some details that would need to be debated, this would eliminate
> (most) everything that the compiler defines for you. Thus, if you wanted
> something, you would have to define it or use " = default" (yes, I am aware
> that would require extending "= default" to more items - seems OK to me).
> The obvious advantage is that the compiler now provides some help, in that
> using something that is not defined will yield a compiler error.

I do not say anything about wether this is useful or not but I dislike the
gracious co-opting of explicit so lets open up the bikeshed painting session.

I would propose that you reuse "= delete" like this:

class T = delete : private B { };

The point of is that it it more logical to use "= delete" than "explicit" to
state that all defaulted members are deleted.

/MF


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