Regression in SWIG 1.3.39

[nitro-4]

Hello,

after upgrading from 1.3.36 my wrappers broke, caused by the change below:

http://swig.svn.sourceforge.net/viewvc/swig/trunk/Lib/swig.swg?r1=11006&r2=11007

in particular the removal of SwigValueWrapper(const T& t) .

I am wrapping a function like

void func( MySmartPtr<SomeType> someParameter = 0 );

Which causes code like

SwigValueWrapper< MySmartPtr< SomeType > > arg1 = (SwigValueWrapper<  
MySmartPtr< SomeType > >) 0 ;

to be generated. This fails (under msvc 2008) with an error like

error C2440: 'conversion': cannot convert from 'int' to  
'SwigValueWrapper<T>'

This is obvious, as only the constructor of MySmartPtr accepts 0, the  
constructor of SwigValueWrapper doesn't accept 0 as a constructor argument.

Unless there's a compelling reason against this, I vote to reintroduce the  
SwigValueWrapper(const T& t) constructor.

Thanks,
-Matthias

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[wsfulton]

Nitro wrote:

> Hello,
>
> after upgrading from 1.3.36 my wrappers broke, caused by the change below:
>
> http://swig.svn.sourceforge.net/viewvc/swig/trunk/Lib/swig.swg?r1=11006&r2=11007
>
> in particular the removal of SwigValueWrapper(const T& t) .
>
> I am wrapping a function like
>
> void func( MySmartPtr<SomeType> someParameter = 0 );
>
> Which causes code like
>
> SwigValueWrapper< MySmartPtr< SomeType > > arg1 = (SwigValueWrapper<  
> MySmartPtr< SomeType > >) 0 ;
>
> to be generated. This fails (under msvc 2008) with an error like
>
> error C2440: 'conversion': cannot convert from 'int' to  
> 'SwigValueWrapper<T>'
>
> This is obvious, as only the constructor of MySmartPtr accepts 0, the  
> constructor of SwigValueWrapper doesn't accept 0 as a constructor argument.
>
> Unless there's a compelling reason against this, I vote to reintroduce the  
> SwigValueWrapper(const T& t) constructor.
>

I can't get your example function above to generate the
SwigValueWrapper. Please provide a standalone example to reproduce and
then I'll look at reintroducing it.

William

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[nitro-4]

Am 17.06.2009, 00:25 Uhr, schrieb William S Fulton  
<wsf@...>:

> Nitro wrote:
>> Unless there's a compelling reason against this, I vote to reintroduce  
>> the
>> SwigValueWrapper(const T& t) constructor.
>>
> I can't get your example function above to generate the
> SwigValueWrapper. Please provide a standalone example to reproduce and
> then I'll look at reintroducing it.

Attached is a sample which shows the problem.

The swig command line is included as a comment on the very first line of  
the line. I think the crucial part is the "-keyword" flag in combination  
with the forward declaration of MyClass. If you remove any of these two  
the bug does not show up.

Thanks for looking into this.

-Matthias

P.S.: In addition to re-adding the SwigValueWrapper(const T& t)  
constructor I also had to comment SwigValueWrapper(const  
SwigValueWrapper<T>& rhs); I am not sure if that's a good idea, but it  
made the wrapper in my original case compile and work.

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[wsfulton]

Nitro wrote:

> Am 17.06.2009, 00:25 Uhr, schrieb William S Fulton
> <wsf@...>:
>
>> Nitro wrote:
>>> Unless there's a compelling reason against this, I vote to
>>> reintroduce the
>>> SwigValueWrapper(const T& t) constructor.
>>>
>> I can't get your example function above to generate the
>> SwigValueWrapper. Please provide a standalone example to reproduce and
>> then I'll look at reintroducing it.
>
> Attached is a sample which shows the problem.
>
> The swig command line is included as a comment on the very first line of
> the line. I think the crucial part is the "-keyword" flag in combination
> with the forward declaration of MyClass. If you remove any of these two
> the bug does not show up.
>
> Thanks for looking into this.
>
> -Matthias
>
> P.S.: In addition to re-adding the SwigValueWrapper(const T& t)
> constructor I also had to comment SwigValueWrapper(const
> SwigValueWrapper<T>& rhs); I am not sure if that's a good idea, but it
> made the wrapper in my original case compile and work.

Matthias, the real problem is that SwigValueWrapper is being used when
it shouldn't be used. What triggers it off is the compactdefaultargs
feature, which -keyword turns on. The code being generated is something
like:

SwigValueWrapper< MySmartPtr< MyClass > > arg1 = (SwigValueWrapper<
MySmartPtr< MyClass > >)0;

whereas if the compactdefaultargs feature is not used, the generated
code is:

SwigValueWrapper< MySmartPtr< MyClass > > arg1 ;

Clearly the 2nd case requires SwigValueWrapper to work around a missing
default constructor, whereas the first case does not call the default
constructor. Because the 1st case does not require a work around for a
missing default constructor, SwigValueWrapper should not be used. The
svn version fixes this. SwigValueWrapper should not have a copy
constructor or any other type of constructor as it should only be used
for default constructing an object.

William

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