C++ To Python

Good morning,


I have a question to get my bearing (new to swig).

Context: C++ to Python.

Say I have a factory method in C++ `std::vector<shared_ptr<Foo>> 
makeFooVec()` and that I already exposed `Foo` (a C++ class) via SWIG as 
well. I want to be able to invoke the factory method and get back an 
array of _Python Proxy objects_ on the `Foo` instances in the C++ 
vector. It seems that `typemaps` are the answer. I'm assuming that 
others must have solved that already.

Any suggestion on how to go ? (I read the documentation as well as this 
slide deck (https://www.dabeaz.com/SwigMaster/SWIGMaster.pdf) which 
nudged me in the direction of typemaps.

I did make some progress (relayed below) and I can share what didn’t 
quite work. The above is a simplification of the real code (I really 
have a sub-class of `std::vector`,  a custom smart pointer type 
(`handle_ptr<T>`) and `Foo` is really a class `var<int>` …  but the 
above should convey the essence). As you might expect, I’m not getting 
what I want from the current wrapper.

Specifically:

1. The wrapper produces an PySwigObject for the std::vector<…>, not an 
instance of the type I specified in the %template. When I see is:

```
<Swig Object of type 'EVec< handle_ptr< var< int > >,stl::StackAdapter< 
handle_ptr< var< int > >,handle_ptr< Storage > > > *' at 0x107851b70>
```

Where EVec is the subtype of `std::vector`. So I didn’t get a python 
array for my C++ vector (But there is a wrapper for it in the generated 
.py file!). If I try to print(dir(x)) where `x` is that vector, I see:

```
['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', 
'__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', 
'__init__', '__init_subclass__', '__int__', '__le__', '__lt__', 
'__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', 
'__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'acquire', 
'append', 'disown', 'next', 'own']
```

which is not the API of an array in python.

If I do `print(type(x))` I get:

```
<class 'SwigPyObject'>
```

Which is not the expected outcome. So the factory method returned a 
“raw” SwigPyObject and didn’t proxy it. Here is the C++ API for 
it:

```
namespace Factory {
    …
    EVec<var<int>::Ptr,alloci> intVarArray(CPSolver::Ptr cps,int sz,int 
min,int max);
    …
}
```

And I do have a %template for its return type

```
%template(VecVarInt)  
std::vector<handle_ptr<var<int>>,stl::StackAdapter<handle_ptr<var<int>>,handle_ptr<Storage>>>;
%template(EVecVarInt) 
EVec<handle_ptr<var<int>>,stl::StackAdapter<handle_ptr<var<int>>,handle_ptr<Storage>>>;
```

Note that `VecVarInt` is the vanilla `std::vector` (the parent class of 
`EVec`) and I used template on both `std::vector` and
`EVec`. (`var<int>` is the `Foo` I’m talking about).


2. Besides, The things embedded in that object are not proxies to those 
`Foo` (`var<int>` in the above).

Hence two questions:

- How do I get SWIG to wrap the result of the factory method property ?
- How do I get SWIG to generate a container that holds proxies to the 
objects inside  the vector ?

Any pointers most welcomed!

Thanks & Happy New Year.

—
  Laurent

_______________________________________________
Swig-user mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/swig-user