Re: Throwing auto_ptr
* James Kanze:
On Apr 2, 12:09 pm, "Alf P. Steinbach" <a...@start.no> wrote:
* Thomas Kowalski:
I currently was thinking whether the following is a good idea:
I want to have something like an auto_ptr that checks during the
dereferencing whether the pointer is null and throws something like a
NullPointerException. Does someone have some experiences with
something like this? In general is it a good idea at all?
Better have it terminate the program. Even better, do the checking only
in the constructor and make it immutable.
Isn't that just what a reference does.
Nope. A reference does not provide any guaranteed null-reference
checking: it's like a cast in that it says "I guarantee that this
assumption (of validity) holds". And it doesn't support checking for
nullness yourself, for if you have a null-reference on hand you're
already in Undefined Behavior land.
A smart pointer can provide both guaranteed null-pointer checking and
the option of checking that yourself, and in addition, a smart-pointer
can add any functionality, such as argument-independent pre- and
post-actions for calls on the pointee object, or e.g. information
/about/ the pointee object.
IMHO references are for when you're guaranteeing validity, based on
existing validity guarantees, whereas class type wrappers such as smart
pointers are for when you need to enforce that guarantee.
(Some compilers omit the
checking, but there's no reason to. From a quality of
implementation point of view, they should check. I guess most
just consider that the code's going to blow up fast enough
anyway.)
I agree that there are situations where a compiler could and ideally
should insert checking of pointer dereferencing, if instructed to do so
by e.g. compiler options, such as when initializing a reference.
Correctness is far more important than performance, but I wouldn't like
a compiler to add such checks by default -- then better use C# or Java
or some other language that doesn't have efficiency as a main feature
and isn't based on "don't pay for what you don't use".
However, a smart pointer is compiler-independent and allows such
checking to be applied at much finer granularity than a complete app.
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