[Issue 6770] New: inout is allowed on fields

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6770

           Summary: inout is allowed on fields
           Product: D
           Version: D2
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: schveiguy at yahoo.com


--- Comment #0 from Steven Schveighoffer <schveiguy at yahoo.com> 2011-10-05 06:48:16 PDT ---
inout cannot be allowed to be an attribute for fields, since inout is
implicitly cast at the end of an inout function.

With this allowance, I can obtain a mutable pointer to an inout field, even
though it should be treated as const:

struct S
{
    inout(int) x;

    inout(int)* foo() inout
    {
        return &x;
    }
}

void main()
{
    S s;
    auto xp = s.foo();
    *xp = 3;
    assert(s.x == 3);
}

inout should be a temporary condition, only allowed for stack-stored types. 
But fields can be placed outside the stack, since you can place any struct or
class outside the stack.

Alternatively, you could be able to declare a struct field as inout, and then
not allow that struct type to ever be placed anywhere but the stack.  But I do
not see a good use case for that feature.

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