Can signatures be made simpler and error messages be made better?

[Adolphus Greenholt]

On Saturday, 12 June 2021 at 08:13:42 UTC, Ola Fosheim Grøstad 
wrote:
> One of the things I don't like about C++ is that signatures 
> often end up being complex. Sadly, D2's signatures are even 
> more complex (D1 had an edge on C++ there).
>
> Why not simply move "linting" information to a separate line 
> and keep the "first line" of function definitions clean.
>
> E.g. to require the return value, and c.x to have the same 
> lifetime:
> ```
> int myfunc(A a, ref T c)
> lifetime(return,c.x)
> {
>   body
> }
> ```
>
> Or introduce a new operator £ that takes the lifetime of an 
> object, which I think is even better:
>
> ```
> int myfunc(A a, B b, ref T c)
> require(£return==£a.x)
> {
>   body
> }
> ```
>
> This would also allow specifying destruction order
> ```
> require(£b < £a.x)
> ```
>
> Or are there things that needs to be expressed about life times 
> that cannot work with such a scheme?
>
> I also think a scheme like this should allow library authors to 
> give names to individual requirements and invariants.
>
> That would allow better error messages, maybe even custom error 
> handlers, e.g.:
>
> ```
> …
> invariant outofbounds { tests }
> …
> require lifetimes (…)
> …
> __interpret_compilation_error outofbounds (context) {
>    if (context.xyz such and such)
>    return "This failed because..."<a 
> href="https://www.mygiftcardsite.one/">My Gift Card Site</a>
> }
>
> ```

Electronic Signatures and Digital Signatures sound synonymous but 
More loosely, e-signatures are used to refer to any signature 
that is The existence of notaries was invented to help address 
these very valid concerns and can be