An interesting consequence of safety requirements

[Leandro Lucarella]

Andrei Alexandrescu, el  4 de noviembre a las 11:24 me escribiste:
> Something just dawned on me: in safe mode, struct static member
> functions will be preferred to struct non-static member functions.
> 
> Why?
> 
> Consider:
> 
> struct List(T) {
>     T payload;
>     List * next;
> 
>     void prepend(List * newNode) {
>         newNode.next = &this;
>     }
> }
> 
> This code can't make it in safe mode because it takes the address of
> this. In general, the compiler must assume that you might have
> created a List object on the stack, e.g.:
> 
> List * someFun() {
>     List local;
>     List * lst = new List;
>     local.prepend(lst);
>     return lst;
> }
> 
> Now even if there is no ostensible local address taking, the code is
> in error because it has escaped the address of a local.
> 
> So prepend() cannot be compiled. The way to make it compile in safe mode is:
> 
> 
> struct List(T) {
>     T payload;
>     List * next;
> 
>     static void prepend(List * zis, List * newNode) {
>         newNode.next = zis;
>     }
> }
> 
> Now the code compiles and is actually safe because it is impossible
> to pass the address of a local into prepend.
> 
> So get ready to use static a lot more ;o).

Or maybe th compiler should rewrite local.prepend(lst); as:
auto this_ = &local;
f(*_this);

Then the compiler can detect when taking the address of local is not
legal as it will do if you write the function as static.

-- 
Leandro Lucarella (AKA luca)                     http://llucax.com.ar/
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