Re: 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.