Failure to bind vector of smart pointers

[grayj2]

Starting to use litgen to make bindings and ran into an issue when using vectors of smart points. litgen does not seem to interpret vectors of smart pointers correctly.

example.h

#include <vector>

class ClassA {};

class ClassB {
  public:
    std::vector<std::shared_ptr<ClassA>> vec_shared_ptrs;
    std::vector<std::unique_ptr<ClassA>> vec_unique_ptrs;
    std::vector<ClassA> vec;
    std::shared_ptr<ClassA> shared_ptr;
    std::unique_ptr<ClassA> unique_ptr;
};

resulting stubs with no options specified which are obviously wrong and do not throw any errors when generating other than black formatting errors.

class ClassA:
    def __init__(self) -> None:
        """Autogenerated default constructor"""
        pass

class ClassB:
    vec_shared_ptrs: std.vector<ClassA>
    vec_unique_ptrs: std.vector<ClassA>
    vec: List[ClassA]
    shared_ptr: ClassA
    unique_ptr: ClassA
    def __init__(self) -> None:
        """Autogenerated default constructor"""
        pass

I was able to get around this and get something more expected using the following type replacement option and regex

    options = litgen.LitgenOptions()
    options.type_replacements.add_first_replacement(r"std::vector<std::(?:unique_ptr|shared_ptr)<(.*)>>", r"std::vector<\1>")

This results in stubs looking like this

class ClassA:
    def __init__(self) -> None:
        """Autogenerated default constructor"""
        pass

class ClassB:
    vec_shared_ptrs: List[ClassA]
    vec_unique_ptrs: List[ClassA]
    vec: List[ClassA]
    shared_ptr: ClassA
    unique_ptr: ClassA
    def __init__(self) -> None:
        """Autogenerated default constructor"""
        pass

Im not sure if this is best approach or just the naive solution. Considering how smart pointers of a class and a vector of classes gets bound, I would expect to get this result. Would appreciate your insight.

[pthom]

Binding smart pointers with pydind11 is complex.

Concerning the stubs, your solution was a step in the right direction.
I fixed it inside cpp_to_python, by applying the changes to unique_ptr and shared_ptr before vector:

litgen/src/litgen/internal/cpp_to_python.py

Lines 517 to 520 in 5c0740d

	\bstd::unique_ptr<(.*?)> -> \1
	\bstd::shared_ptr<(.*?)> -> \1
	\bstd::vector\s*<\s*([\w:]*)\s*> -> List[\1]
	\bstd::array\s*<\s*([\w:]*)\s*,\s*([\w:]*)\s*> -> List[\1]

Now, concerning your usage:

• publishing a member under the form of unique_ptr (or a vector<unique_ptr> might lead to multiple issues (as copying it as reference inside python is prohibited)
• it works for shared_ptr. However, you need to change the holder type.

For an example, see this integration test:

https://github.com/pthom/litgen/blob/main/src/litgen/integration_tests/mylib/smart_ptr.h

And its bindings:

https://github.com/pthom/litgen/blob/main/src/litgen/integration_tests/mylib/smart_ptr.h.pyi

Where I had to specify the holder type for SmartElem

litgen/src/litgen/integration_tests/autogenerate_mylib.py

Lines 53 to 54 in 5c0740d

	# For smart_ptr_test: SmartElem will be held in (vector of) shared_ptr
	options.class_held_as_shared__regex = "^SmartElem$"

Read here the doc for class_held_as_shared__regex:

litgen/src/litgen/options.py

Lines 405 to 420 in 5c0740d

	# class_held_as_shared__regex:
	# Regex specifying the list of class names that should be held using std::shared_ptr in the generated bindings.
	#
	# **Purpose:**
	# By default, pybind11 uses `std::unique_ptr` as the holder type for bound classes.
	#
	# **When to Use:**
	# If your C++ code uses `std::shared_ptr` to manage instances of a class (e.g., as member variables, return types,
	# or parameters), and you expose that class to Python, you need to ensure that pybind11 uses `std::shared_ptr` as
	# the holder type for that class.
	#
	# **References:**
	# - [pybind11 Documentation: Smart Pointers](https://pybind11.readthedocs.io/en/stable/advanced/smart_ptrs.html)
	# - [Understanding Holder Types in pybind11](https://pybind11.readthedocs.io/en/stable/advanced/classes.html#custom-smart-pointers)
	class_held_as_shared__regex: str = ""

[pthom]

Note: you will need to update litgen to the latest commit

[grayj2]

Thank you for the updates! This did the trick.

Understood about the caveats on smart pointers. Mainly just tinkering at this point to understand how to use litgen. So far it seems pretty straight forward.