On Tue, 26 Apr 2011 20:15:45 -0400, Daniel Gibson <metalcae...@gmail.com>
wrote:
Am 27.04.2011 02:03, schrieb Steven Schveighoffer:
On Tue, 26 Apr 2011 19:45:21 -0400, Daniel Gibson
<metalcae...@gmail.com> wrote:
I just noticed something regarding clear():
struct Bar { ... }
Bar *b = new Bar();
This compiles without any warning, but doesn't call the destructor:
clear(b);
This compiles without any warning and actually does what you'd expect,
i.e. calls destructor:
clear(*b);
Is this behavior expected/wanted? If not: Is it a known bug? I couldn't
find it in the bugtracker, but maybe I searched for the wrong keywords.
Let's start with class references. Because class references cannot be
separated from its reference, you have to finalize the class when
finalizing the reference, because there's no way to say "clear what this
reference refers to" vs. "clear this reference". So you have to give a
way to finalize a class instance.
With pointers, however, you can specify as you say, whether you want to
clear the pointer or the struct itself.
Now, is it much useful to clear a pointer without clearing what it
points to? I'd say no, clearing a pointer is as easy as doing ptr =
null. So I'm thinking, it should be filed as a bug.
The obvious thing to decide is, what should be done on references to
references? If you clear a double pointer, should it go through both
pointers? Or a pointer to a class reference?
I'd say no, but you have to take extra steps to ensure it is this way.
-Steve
IMHO clear isn't needed for anything but structs and Objects.
For any simple type or pointer you can just write x = x.init; instead of
clear(x) or, as you already mentioned, x=null; for pointers.
It is useful for it to work for generic code.
AFAIK the main purpose of clear() is to explicitly call the destructor -
and that only makes sense for structs and classes.
Allowing it for other types (especially pointers) just sneaks in
non-obvious bugs, especially when it's considered a replacement for
delete (which calls the destructor for both Object a *struct).
I'm not sure it introduces subtle bugs for things besides pointers.
Clearing an int should be harmless.
BTW: clear() has often been mentioned in this NG but isn't documented in
the Phobos documentation (which is no surprise because clear() doesn't
have doc-comments).
So I guess I'll report this as a bug.
If you mean that clear has no docs, I already reported that.
http://d.puremagic.com/issues/show_bug.cgi?id=5855
Feel free to report the enhancement request for clear to dereference
pointers.
-Steve
