Re: [Swig-user] Implicit conversion in Ruby?

[Bob H. <bh...@co...>]

On 12/14/2013 9:06 AM, Macumber, Daniel wrote:
>
> Thanks for looking into this Bob!  I think you are right that I want to do
> an explicit conversion, but I am not understanding how to do that with
> typemaps.  The problem I am having is that in ruby the input type is
> String.  SWIG has a map somewhere that converts String to std::string, I
> want to add one that converts String to path.  I've tried looking in the
> files related to strings in \SWIG\Lib\ruby\ but I am not seeing anything
> that makes sense to me.
>
>  
>
>   1) Error:
>
> test_funcOnlyTakesAPath(Path_Test):
>
> TypeError: Expected argument 0 of type openstudio::path const &, but got String
>
> "./here"
>
>         in SWIG method 'funcOnlyTakesAPath'
>
>     Path_Test.rb:48:in `funcOnlyTakesAPath'
>
>     Path_Test.rb:48:in `test_funcOnlyTakesAPath'
>

I can't couch this in terms of Ruby, because I've never wrapped that
language.  I have done Python extensively, so here is a SWIG typemap that
performs the conversion you're after.

I've defined a simple class:

    class path
    {
    public:
        path(const std::string& str) {}
    };

and a function prototype:

    void funcOnlyTakesAPath(const path& p);

in the same header for SWIG to process.

In my SWIG interface file, I have the following typemap that converts a Python
None or string into a path class instance:

    %typemap(in) const path& {
        $1 = NULL;
        if($input == Py_None)
            $1 = new path("");
        else if(PyString_Check($input))
            $1 = new path(PyString_AsString($input));
        else
            SWIG_fail;
    }

    %typemap(freearg) const path& {
        if($1) delete $1;
    }

In Python, invoking this as:

    funcOnlyTakesAPath('./here')

functions as you want, with an instance of the path class being constructed
and passed to the internal C++ funcOnlyTakesAPath() function as a 'const
path&' type.  You just need to replace the Python API idioms for Ruby in this
code to detect and convert the types.