DIP1000: Scoped Pointers (Discussion)

[Walter Bright via Digitalmars-d]

On 8/14/2016 7:37 AM, Dicebot wrote:
> struct Container
> {
>     int data;
>
>     static struct Range
>     {
>         int* pdata;
>         // range methods skipped for clarity ..
>     }
>
>     Range asRange ( )
>     {
>         return Range(&this.data);
>     }
> }
>
> void main ( )
> {
>     Container container;
>
>     import std.stdio;
>     writeln(container.asRange()); // case 1, OK
>
>     scope r = container.asRange(); // case 2, OK
>     auto r = container.asRange(); // case 3, not OK
> }


A great example. Let's analyze by peeling back the syntactic sugar:

----
'container' is a stack variable

'container.int' is a stack variable

'asRange()' returns an instance of 'Range' which is a stack variable, call it 
'range'

'range.pdata' is a stack variable

Range range.pdata = &container.data; // range is inferred as 'scope' because
                                      // container.data is a stack variable

auto r = range; // r is inferred as 'scope' because 'range' is 'scope'
----

It's a bit advanced, but it falls entirely in the DIP rules and is workable with 
some implementation effort (not sure how much).

The idea is, if something is ultimately a stack variable, the scope rules apply.