Am 24.09.2011, 07:28 Uhr, schrieb Mehrdad <wfunct...@hotmail.com>:
On 9/23/2011 8:11 PM, Jonathan M Davis wrote:
On Friday, September 23, 2011 19:42:24 Walter Bright wrote:
On 9/23/2011 6:55 PM, Jonathan M Davis wrote:
True, but it doesn't just happen. You have to choose to make a
variable
mutable.
Which you *must* do for logical const. And, of course, anything beyond
the
first level is not const at all, and there's NO WAY to say it is const.
_Some_ effort must be put in to circumvent const. Until you do that,
const protects it from be changed.
There's no way to detect who or what is changing it.
By no means am I claiming that C++'s const is without flaws. I'm just
claiming that it's not worthless, and you seem to be claiming that
it's
worthless.
I think it is worthless because:
1. a number of C++ programmers I've talked to who relied on being able
to
change const objects and insisted that was a feature.
2. the pervasive misconceptions about what C++ const guarantees and
what it
doesn't, even among C++ committee members.
3. the complete uselessness C++ const has for multithreaded
programming.
4. the pervasiveness of the Double Checked Locking Bug, which is one
of the
consequences of (3).
5. it's head-const only. Anything beyond one level of indirection is
completely const-free. Only trivial data structures are one level.
Well, I grant you that all of those are issues, but I don't think that
they
makes C++'s const worthless. Const has caught bugs in my code for me. I
have
found it to be useful in the projects that I've worked on. So, we're
obviously
just going to have to agree to disagree on this, and I think that a lot
of C++
programmers are going to disagree with you (including many who
understand
exactly what const does and doesn't guarantee).
- Jonathan M Davis
+1 gotta agree 100% with Jon here. (Hey, is that the first time?! :P) I
wouldn't believe anyone for 1 second if he said he's used const in his
code and it never caught an error for him (or if it introduced more than
it caught).
Of course it does, because these bugs were logical bugs, an area where
logical const is a perfect match. (You don't need guarantees, just the
semantic analysis at compile time.)
