[Dlang-internal] DIP1000 discussion and testing

[Mathias Lang via Dlang-internal]

On Saturday, 22 October 2016 at 07:19:11 UTC, Walter Bright wrote:
> On 10/21/2016 1:30 AM, pineapple wrote:
>> There's this big language enhancement in the pipeline
>
> But it's not big.
>
> It's the same as 'return ref', which is already there, except 
> it's 'return scope'. The examples on how it works all boil down 
> to a couple lines of code.

Most people seem to disagree with that opinion.

I was looking at the DIP, and checked out the P.R. branch to test 
it, and I cannot see how it could work if `scope` is not 
transitive.
It is just pushing the problem one level down.

For example:

```
alias FunDG = void delegate () @safe;

struct Escaper
{
     FunDG DG;
}

FunDG escapeDg1 (scope FunDG d) @safe
{
     Escaper e;
     e.DG = d;
     return e.DG;
}
```

This compiles, and escapes a `scope delegate`.
Used `./src/dmd -transition=safe -dip25 -run test.d` to compile, 
on commit:
`48b7815 - (HEAD, walter/return-scope) add lifetime checks (9 
days ago) <Walter Bright>`. Did I miss something ?


Also, as others already mentioned, the DIP is quite confusing.

I read the whole thread and AFAICS people got confused because of 
https://github.com/dlang/DIPs/blob/master/DIPs/DIP1000.md#escaping-via-return which mentions that "taking the address of a local [...] is restrictive." and continue with "The `scope` storage class was introduced which annotates the pointer.", which doesn't quite relate to the previous sentence if scope is not meant to remove this restriction.
The examples also use a mix of `@safe` and non-annotated 
function, which doesn't help understanding since it's explicitly 
stated that those checks are only done in @safe code (why?).
Finally, I agree with Dicebot that having scope infered when the 
type is specified is extremely confusing, and makes writing test 
cases, and code in general, much more complicated.