[Dlang-internal] DIP1000 discussion and testing: borrowing a range

[Walter Bright via Dlang-internal]

On 10/20/2016 9:44 AM, Dicebot wrote:
> This compiles too:
>
> ```
> int* x;
>
> @safe unittest
> {
>     @safe static struct S
>     {
>         int data;
>
>         int* borrow () return scope @trusted {
>             return &this.data;
>         }
>     }
>
>     S instance;
>     x = instance.borrow();
> }
> ```
>
> Now, _this_ must be wrong, right?


It compiles because you added '@trusted' to the bad boy function, disabling the 
check preventing taking the address of a 'ref'. The compiler has no reason to 
believe that the return value of instance.borrow() has any relationship to 
'instance' - it @trusted the programmer to not do that!

The practical result is that a container that is passed by ref can only control 
its uses by returning by ref, not by *.