Struct should be invalid after move

[Alex]

On Tuesday, 27 November 2018 at 14:37:40 UTC, Stanislav Blinov 
wrote:
> On Tuesday, 27 November 2018 at 13:17:24 UTC, Alex wrote:
>
> For compile-time checks, sure, as it is a convenient way to get 
> at the underlying type. But that's all that is.
>
> Right now we have to resort to runtime checks. Which is 
> hilarious considering we *can* disable default construction, 
> thereby asserting that .init is indeed an invalid state.
>

Ok... so. Without default construction,

int i;
and
int i = void;

become the same. But you won't be able to prevent it from being 
an int, right?
How would you detect an invalid state in this case?

>
> What Sebastiaan proposes is for there to be *no* behavior at 
> all, as using an invalid value would become a compile-time 
> error. Which would mean one wouldn't need extraneous run-time 
> checks.

I assume, that detecting invalid states becomes harder as types 
become simpler. And, it depends strongly on the application, 
whether a value is considered invalid... Doesn't Typedef already 
allow this functionality?