Re: [boost] [local_function] how bad is this `static_cast<>`?

Subject: Re: [boost] [local_function] how bad is this `static_cast<>`?
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-09-09 12:13:03

AMDG

Lorenzo Caminiti wrote:
> How bad is the `static_cast<>` below?
>
> struct c {
>     void g() {}
>
>     void f() {
>         struct l: c { // Local function class wrapper.
>             void body() {
>                 g(); // Usual implicit `this` access.
>                 this->g(); // Usual explicit `this` access.
>             }
>         };
>
>         static_cast<l*>(this)->body(); // *** HOW BAD IS THIS
> `STATIC_CAST<>`? ***
>     }
> };
>
> Could Boost.LocalFunction internally use such a technique when a
> special configuration macro is #defined by the users?
>
> IMO, if this `static_cast<>` can really corrupt memory on some
> systems/compilers, maybe Boost.LocalFunction should *never* use it.
> Otherwise, what would the documentation say "WARNING: If you #define
> this configuration macro, memory could be corrupted in some unknown
> way on some unknown combination of systems/compilers..." -- it's like
> providing a self-destruction button with a random countdown sequence
> via the configuration macro! What do you think?
>   

The problem with code like this is that it can cause the optimizer
to make incorrect assumptions and miscompile the code.  I
believe that this has been observed with gcc.

In Christ,
Steven Watanabe