Steven Schveighoffer <schvei...@yahoo.com> wrote:
class C
{
private Mutable!(int) cache = -1;
int expensiveFunction() const { return cache == -1 ? cache =
_expensiveFunctionImpl() : cache; }
private int _expensiveFunctionImpl() const {...}
}
If this is undefined, then something like this cannot be relied on,
even when performance is critical.
-Steve
I really can't see how the compiler could make that work, without
destroying most of the benefits of const. For example, if that code is
legal, it disallows most const-related optimisation.
Why not? What possible optimization can the compiler do here? Mutable
has an assign operation that is labeled as const, it should be callable
by the compiler.
I haven't really seen what const optimizations can be, so maybe an
example (even if unimplemented) is helpful.
The compiler may decide to store the value of cache in a register, and
use that value instead of fetching it after _expensiveFunctionImpl is
called. That's the simplest example I could come up with.
--
Simen
