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From: Martin B. on 11 Nov 2009 02:50
Hi all.

// With a pointer I can do:
if(MyWhatever* pX = get_whatever()) {

}

However, for this to work with a shared pointer (shared_ptr or
scoped_ptr from boost) I have to do:
if(shared_ptr<MyWhatever> pX = shared_ptr<MyWhatever>(get_whatever())) {

}

This is ugly (and presumably could also add some runtime overhead).

Is there a better way?

br,
Martin

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From: Ulrich Eckhardt on 11 Nov 2009 08:06
Martin B. wrote:
> // With a pointer I can do:
> if(MyWhatever* pX = get_whatever()) {
>
> }

Correct.

> However, for this to work with a shared pointer (shared_ptr or
> scoped_ptr from boost) I have to do:
> if(shared_ptr<MyWhatever> pX = shared_ptr<MyWhatever>(get_whatever())) {
>
> }

Do you? What is the declaration of get_whatever()? Did you change that to
return a shared_ptr, too? In that case, you could safe yourself the explicit
conversion. If not, you could at least use this syntax:

if(shared_ptr<T> p(get_whatever()))

Which works if I remember correctly.

> This is ugly (and presumably could also add some runtime overhead).
>
> Is there a better way?

Change get_whatever() to return either a boost::shared_ptr or an
std::auto_ptr.

Uli


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From: Martin B. on 11 Nov 2009 15:49
Ulrich Eckhardt wrote:
> Martin B. wrote:
>> // With a pointer I can do:
>> if(MyWhatever* pX = get_whatever()) {
>>
>> }
>
> Correct.
>
>> However, for this to work with a shared pointer (shared_ptr or
>> scoped_ptr from boost) I have to do:
>> if(shared_ptr<MyWhatever> pX = shared_ptr<MyWhatever>(get_whatever())) {
>>
>> }
>
> Do you? What is the declaration of get_whatever()? Did you change that to
> return a shared_ptr, too? In that case, you could safe yourself the explicit
> conversion. If not, you could at least use this syntax:
>
> if(shared_ptr<T> p(get_whatever()))
>
> Which works if I remember correctly.
>

You remember wrongly. I get a compiler error if I try this. (That was
the reason for the post, if that'd work, I'd just change the syntax for
the cases where I use a shared_ptr - I don't mind the missing '=' character)

>> This is ugly (and presumably could also add some runtime overhead).
>>
>> Is there a better way?
>
> Change get_whatever() to return either a boost::shared_ptr or an
> std::auto_ptr.
>

Can't change in this case.

cheers,
Martin

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From: Jeff Flinn on 12 Nov 2009 01:30
Martin B. wrote:
> Hi all.
>
> // With a pointer I can do:
> if(MyWhatever* pX = get_whatever()) {
>
> }
>
> However, for this to work with a shared pointer (shared_ptr or
> scoped_ptr from boost) I have to do:
> if(shared_ptr<MyWhatever> pX = shared_ptr<MyWhatever>(get_whatever())) {
>
> }
>
> This is ugly (and presumably could also add some runtime overhead).
>
> Is there a better way?

typedef shared_ptr<MyWhatever> MyWhateverPtr; // ;-)

if(MyWhateverPtr pX = MyWhateverPtr(get_whatever()))
{
...
}

or even less redundant and more safe: make get_whatever return a
MyWhateverPtr. If you can't modify the get_whatever() wrap it in another
function that returns a MyWhateverPtr.

Jeff



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From: Joshua Maurice on 12 Nov 2009 09:15
On Nov 12, 10:30 am, Jeff Flinn <TriumphSprint2...(a)hotmail.com> wrote:
> Martin B. wrote:
> > Hi all.
>
> > // With a pointer I can do:
> > if(MyWhatever* pX = get_whatever()) {
>
> > }
>
> > However, for this to work with a shared pointer (shared_ptr or
> > scoped_ptr from boost) I have to do:
> > if(shared_ptr<MyWhatever> pX = shared_ptr<MyWhatever>(get_whatever())) {
>
> > }
>
> > This is ugly (and presumably could also add some runtime overhead).
>
> > Is there a better way?
>
> typedef shared_ptr<MyWhatever> MyWhateverPtr; // ;-)
>
> if(MyWhateverPtr pX = MyWhateverPtr(get_whatever()))
> {
> ...
> }
>
> or even less redundant and more safe: make get_whatever return a
> MyWhateverPtr. If you can't modify the get_whatever() wrap it in another
> function that returns a MyWhateverPtr.

Adding a one line helper function to use in one case seems very much
like overkill and obfuscation. What's wrong with the following?

MyWhateverPtr pX(get_whatever());
if(pX.get())
{
//...
}

If you really want to restrict the scope of pX, then add braces:

{
MyWhateverPtr pX(get_whatever());
if(pX.get())
{
//...
}
}

This would be much quicker and easier for me to read then look at the
code and ponder what this function does, only to see it's a near
trivial one liner just to play to your particular liking for putting
declarations in if statements. just my humble opinion.


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