Re: [pygccxml-development] Parameter default value, no type?

[Roman Y. <rom...@gm...>]

On Sun, Jul 13, 2008 at 6:09 PM, Gustavo Carneiro <gjc...@gm...> wrote:
> Hi,
>
> I am trying to wrap methods like this:
>
>
>   void SetMac (std::string type,
>            std::string n0 = "", const AttributeValue &v0 =
> EmptyAttributeValue (),
>            std::string n1 = "", const AttributeValue &v1 =
> EmptyAttributeValue (),
>            std::string n2 = "", const AttributeValue &v2 =
> EmptyAttributeValue (),
>            std::string n3 = "", const AttributeValue &v3 =
> EmptyAttributeValue (),
>            std::string n4 = "", const AttributeValue &v4 =
> EmptyAttributeValue (),
>            std::string n5 = "", const AttributeValue &v5 =
> EmptyAttributeValue (),
>            std::string n6 = "", const AttributeValue &v6 =
> EmptyAttributeValue (),
>            std::string n7 = "", const AttributeValue &v7 =
> EmptyAttributeValue ());
>
> The problem I am having is that class AttributeValue is abstract and cannot
> be instantiated.  Normally in pybindgen I handle default values like this:
>
> PyParameter *pyParam = NULL;
> PyArg_ParseTupleAndKeywords("...|O!", ..., &PyParameter_Type, &pyParam);
> [...]
> CallMyMethod ((pyParam? pyParam->obj : <Param Default Value>));
>
> For instance,, if <Param Default> is ns3::EmptyAttributeValue(), I get a
> compilation error:
>
> debug/bindings/python/ns3_module_helper.cc:83: error: cannot allocate an
> object of abstract type 'ns3::AttributeValue'
> debug/ns3/attribute.h:52: note:   since type 'ns3::AttributeValue' has pure
> virtual functions
>
> One solution to this problem would be the following:
>
> PyParameter *pyParam = NULL;
> <Param Default Type>  paramDefault = <Param Default Value>;
> PyArg_ParseTupleAndKeywords("...|O!", ..., &PyParameter_Type, &pyParam);
> [...]
> CallMyMethod ((pyParam? pyParam->obj : paramDefault));
>
> The above code would compile; I tested.  The problem is that pygccxml does
> not give me the type of the default parameter value, and of course the type
> of the parameter itself is useless in these cases (it is abstract).
>
> Any suggestion would be welcome.

There is a problem with default arguments and gccxml:
http://language-binding.net/pygccxml/upgrade_issues.html#free-and-member-function-default-arguments

I am not sure what can you do, I will give you few links to other
possible solutions:

1. http://www.boost.org/doc/libs/1_35_0/libs/python/doc/v2/overloads.html

2. Second you can ask your users to update default values - pygccxml
supports this functionality.
    May be you will even find some use case, that pygccxml could treat
automaticaly:
    http://language-binding.net/pygccxml/apidocs/pygccxml.parser.patcher-pysrc.html

HTH
-- 
Roman Yakovenko
C++ Python language binding
http://www.language-binding.net/