DIP69 - Implement scope for escape proof references

[Dicebot via Digitalmars-d]

On Tuesday, 9 December 2014 at 22:24:51 UTC, Walter Bright wrote:
>>> front() should return a 'scope ref string'.
>>
>> That seems to contradict your other statement:
>>
>>> A 'scope ref' parameter may not be returned as a 'ref' or a 
>>> 'scope ref'.
>
> Just make it a 'ref' parameter.
>
>
>> Please check `foo()` once more - it needs to accept scope 
>> (ref) to be able to
>> accept ByLine.front as an argument. And it also needs to pass 
>> it down the call
>> chain - but returning `input` by reference is illegal 
>> according to
>> abovementioned rule.
>
> It can still be passed down as a 'ref' parameter.

But as far as I understand the spec it will result it this code 
failing too:

auto r = ["aaa", "bbb", "ccc"].map!foo;
// should compile but will fail because foo returns scope  ref:
string s = r.front;

What I mean is that in current proposal it is impossible to 
transfer scope information down the call chain - either function 
always returns scope ref or never. Which implies the necessity of 
something like `auto scope`...