DIP69 - Implement scope for escape proof references

[Dicebot via Digitalmars-d]

On Monday, 8 December 2014 at 21:12:47 UTC, Walter Bright wrote:
> On 12/8/2014 12:54 PM, Dicebot wrote:
>> struct ByLine
>> {
>>     scope string front();
>>     // ...
>> }
>>
>> auto byLine(File file)
>> {
>>     return ByLine(file);
>> }
>>
>> scope /* ref */ string foo(scope /* ref */ string input)
>> {
>>     return input[1..$];
>> }
>>
>> void main()
>> {
>>     auto r = file.byLine.map!foo;
>>     string s = r.front; // this should not compile
>>     string s = r.front.dup; // this should compile
>>
>>     // how foo signature should look like for this to work?
>> }
>
> 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'.

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.