From: Joe Gottman (jgottman_at_[hidden])
Date: 2005-02-16 20:09:51
"Fernando Cacciola" <fernando_cacciola_at_[hidden]> wrote in message
news:cuvnj8$urr$1_at_sea.gmane.org...
>
> The correct fix along Joe's initial proposal would be:
>
> void assign(optional_base const& rhs)
> {
> if (is_initialized)
> {
> if ( rhs.is_initialized )
> get_impl() = rhs.get_impl();
> else destroy();
> }
> else
> {
> if ( rhs.is_initialized )
> construct(rhs.get_impl());
> }
> }
>
> AFAICS, this code is as safe aliasing-wise as it can be (it handles not
> only the trivial case of this==&rhs but also any other deeper aliasing
> issues)
>
> If no voice is raised I'll proceed with this fix.
While you're at it, you should also fix your other versions of assign().
For instance, consider this flavor of self-assignment:
optional<string> x("foo");
x = *x; // Assign to x from dereferenced x.
This calls the following version of assign:
void assign ( argument_type val )
{
destroy();
construct(val);
}
Thus the code destroys *x, then attempts to assign to *x by dereferencing a
pointer to uninitialized memory, resulting in undefined behavior. This is
should be rewritten as
void assign(argument_type val)
{
if (is_initialized) {
get_impl() = val;
} else {
construct(val);
}
}
Joe Gottman