[QUESTION] Function with pointer to pointer arg

[kumaraditya303]

I am writing a Trampoline class for leveldb Env Class https://github.com/google/leveldb/blob/master/include/leveldb/env.h

class PyEnv : Env
{

public:
    using Env::Env;
    Status NewSequentialFile(const std::string &fname,
                             SequentialFile **result) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,            /* Return type */
            Env,               /* Parent class */
            NewSequentialFile, /* Name of function in C++ (must match Python name) */
            fname,
            result /* Argument(s) */
        );
    }
    Status NewRandomAccessFile(const std::string &fname,
                               RandomAccessFile **result) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,              /* Return type */
            Env,                 /* Parent class */
            NewRandomAccessFile, /* Name of function in C++ (must match Python name) */
            fname,
            result /* Argument(s) */
        );
    }
    Status NewWritableFile(const std::string &fname,
                           WritableFile **result) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,          /* Return type */
            Env,             /* Parent class */
            NewWritableFile, /* Name of function in C++ (must match Python name) */
            fname,
            result /* Argument(s) */
        );
    }
    Status NewAppendableFile(const std::string &fname,
                             WritableFile **result) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,            /* Return type */
            Env,               /* Parent class */
            NewAppendableFile, /* Name of function in C++ (must match Python name) */
            fname,
            result /* Argument(s) */
        );
    }
    bool FileExists(const std::string &fname) override
    {
        PYBIND11_OVERRIDE_PURE(
            bool,       /* Return type */
            Env,        /* Parent class */
            FileExists, /* Name of function in C++ (must match Python name) */
            fname);
    }
    Status GetChildren(const std::string &dir,
                       std::vector<std::string> *result) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,      /* Return type */
            Env,         /* Parent class */
            GetChildren, /* Name of function in C++ (must match Python name) */
            dir,
            result);
    }
    Status RemoveFile(const std::string &fname) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,     /* Return type */
            Env,        /* Parent class */
            RemoveFile, /* Name of function in C++ (must match Python name) */
            fname);
    }
    Status DeleteFile(const std::string &fname) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,     /* Return type */
            Env,        /* Parent class */
            DeleteFile, /* Name of function in C++ (must match Python name) */
            fname);
    }
    Status CreateDir(const std::string &dirname) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,    /* Return type */
            Env,       /* Parent class */
            CreateDir, /* Name of function in C++ (must match Python name) */
            dirname);
    }
    Status RemoveDir(const std::string &dirname) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,    /* Return type */
            Env,       /* Parent class */
            RemoveDir, /* Name of function in C++ (must match Python name) */
            dirname);
    }
    Status DeleteDir(const std::string &dirname) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,    /* Return type */
            Env,       /* Parent class */
            DeleteDir, /* Name of function in C++ (must match Python name) */
            dirname);
    }
    Status GetFileSize(const std::string &fname, uint64_t *file_size) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,      /* Return type */
            Env,         /* Parent class */
            GetFileSize, /* Name of function in C++ (must match Python name) */
            fname,
            file_size);
    }
    Status RenameFile(const std::string &src,
                      const std::string &target) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,     /* Return type */
            Env,        /* Parent class */
            RenameFile, /* Name of function in C++ (must match Python name) */
            src,
            target);
    }
    Status LockFile(const std::string &fname, FileLock **lock) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,   /* Return type */
            Env,      /* Parent class */
            LockFile, /* Name of function in C++ (must match Python name) */
            fname,
            lock);
    }
    Status UnlockFile(FileLock *lock) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,     /* Return type */
            Env,        /* Parent class */
            UnlockFile, /* Name of function in C++ (must match Python name) */
            lock);
    }
    void Schedule(void (*function)(void *arg), void *arg) override
    {
        PYBIND11_OVERRIDE_PURE(
            void,     /* Return type */
            Env,      /* Parent class */
            Schedule, /* Name of function in C++ (must match Python name) */
            function,
            arg,
            arg);
    }
    void StartThread(void (*function)(void *arg), void *arg) override
    {
        PYBIND11_OVERRIDE_PURE(
            void,        /* Return type */
            Env,         /* Parent class */
            StartThread, /* Name of function in C++ (must match Python name) */
            function,
            arg,
            arg);
    }
    Status GetTestDirectory(std::string *path) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,           /* Return type */
            Env,              /* Parent class */
            GetTestDirectory, /* Name of function in C++ (must match Python name) */
            path);
    }
    Status NewLogger(const std::string &fname, Logger **result) override
    {
        PYBIND11_OVERRIDE_PURE(
            Status,    /* Return type */
            Env,       /* Parent class */
            NewLogger, /* Name of function in C++ (must match Python name) */
            fname, result);
    }
    uint64_t NowMicros() override
    {
        PYBIND11_OVERRIDE_PURE(
            uint64_t,     /* Return type */
            Env,          /* Parent class */
            NowMicros, ); /* Name of function in C++ (must match Python name) */
    }
    void SleepForMicroseconds(int micros) override
    {
        PYBIND11_OVERRIDE_PURE(
            void, /* Return type */
            Env,  /* Parent class */
            SleepForMicroseconds,
            micros);
    }
};

Compiler:
Copyright (C) Microsoft Corporation. All rights reserved.

16.8.3.61104
But it errors out while compiling with error:

running build_ext
building 'leveldb' extension
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29333\bin\HostX86\x64\cl.exe /c /nologo /Ox /W3 /GL /DNDEBUG /MD -I./third_party/leveldb/include/ -I./third_party/leveldb/port/ -I./third_party/leveldb/util/ -I./third_party/leveldb/ -I./third_party/snappy/ -I./third_party/snappy/build/ -I./third_party/pybind11/include/ -IC:\Users\Kumar Aditya\AppData\Local\Programs\Python\Python39\include -IC:\Users\Kumar Aditya\AppData\Local\Programs\Python\Python39\include -IC:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29333\include -IC:\Program Files (x86)\Windows Kits\10\include\10.0.18362.0\ucrt -IC:\Program Files (x86)\Windows Kits\10\include\10.0.18362.0\shared -IC:\Program Files (x86)\Windows Kits\10\include\10.0.18362.0\um -IC:\Program Files (x86)\Windows Kits\10\include\10.0.18362.0\winrt -IC:\Program Files (x86)\Windows Kits\10\include\10.0.18362.0\cppwinrt /EHsc /Tp./leveldb/leveldb.cpp /Fobuild\temp.win-amd64-3.9\Release\./leveldb/leveldb.obj -DSNAPPY -DLEVELDB_PLATFORM_WINDOWS
leveldb.cpp
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(870): warning C4180: qualifier applied to function type has no meaning; ignored
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(946): note: see reference to class template instantiation 'pybind11::detail::type_caster_base<type>' being compiled
        with
        [
            type=void (const leveldb::Slice &,void *)
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1996): note: see reference to class template instantiation 'pybind11::detail::type_caster<void (const leveldb::Slice &,void *),void>' being compiled
./third_party/pybind11/include/pybind11/pybind11.h(166): note: see reference to class template instantiation 'pybind11::detail::argument_loader<Class *,const leveldb::Slice &,void *,size_t,void (__cdecl *)(const leveldb::Slice &,void *)>' being compiled
        with
        [
            Class=leveldb::Cache
        ]
./third_party/pybind11/include/pybind11/pybind11.h(85): note: see reference to function template instantiation 'void pybind11::cpp_function::initialize<pybind11::cpp_function::{ctor}::<lambda_7ea5e8ab80bc2d73cc10c3d37f9940e8>,Return,Class*,const leveldb::Slice&,void*,size_t,void(__cdecl *)(const leveldb::Slice &,void *),pybind11::name,pybind11::is_method,pybind11::sibling,pybind11::return_value_policy>(Func &&,Return (__cdecl *)(Class *,const leveldb::Slice &,void *,size_t,void (__cdecl *)(const leveldb::Slice &,void *)),const pybind11::name &,const pybind11::is_method &,const pybind11::sibling &,const pybind11::return_value_policy &)' being compiled
        with
        [
            Return=leveldb::Cache::Handle *,
            Class=leveldb::Cache,
            Func=pybind11::cpp_function::{ctor}::<lambda_7ea5e8ab80bc2d73cc10c3d37f9940e8>
        ]
./third_party/pybind11/include/pybind11/pybind11.h(1317): note: see reference to function template instantiation 'pybind11::cpp_function::cpp_function<Return,leveldb::Cache,const leveldb::Slice&,void*,size_t,void(__cdecl *)(const leveldb::Slice &,void *),pybind11::name,pybind11::is_method,pybind11::sibling,pybind11::return_value_policy>(Return (__cdecl leveldb::Cache::* )(const leveldb::Slice &,void *,size_t,void (__cdecl *)(const leveldb::Slice &,void *)),const pybind11::name &,const pybind11::is_method &,const pybind11::sibling &,const pybind11::return_value_policy &)' being compiled
        with
        [
            Return=leveldb::Cache::Handle *
        ]
./leveldb/leveldb.cpp(409): note: see reference to function template instantiation 'pybind11::class_<leveldb::Cache,PyCache> &pybind11::class_<leveldb::Cache,PyCache>::def<leveldb::Cache::Handle*(__cdecl leveldb::Cache::* )(const leveldb::Slice &,void *,size_t,void (__cdecl *)(const leveldb::Slice &,void *)),pybind11::return_value_policy>(const char *,Func &&,const pybind11::return_value_policy &)' being compiled
        with
        [
            Func=leveldb::Cache::Handle *(__cdecl leveldb::Cache::* )(const leveldb::Slice &,void *,size_t,void (__cdecl *)(const leveldb::Slice &,void *))
        ]
./leveldb/leveldb.cpp(418): note: see reference to function template instantiation 'pybind11::class_<leveldb::Cache,PyCache> &pybind11::class_<leveldb::Cache,PyCache>::def<leveldb::Cache::Handle*(__cdecl leveldb::Cache::* )(const leveldb::Slice &,void *,size_t,void (__cdecl *)(const leveldb::Slice &,void *)),pybind11::return_value_policy>(const char *,Func &&,const pybind11::return_value_policy &)' being compiled
        with
        [
            Func=leveldb::Cache::Handle *(__cdecl leveldb::Cache::* )(const leveldb::Slice &,void *,size_t,void (__cdecl *)(const leveldb::Slice &,void *))
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(883): warning C4180: qualifier applied to function type has no meaning; ignored
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(904): warning C4180: qualifier applied to function type has no meaning; ignored
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(911): warning C4180: qualifier applied to function type has no meaning; ignored
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1836): error C2665: 'pybind11::detail::type_caster_base<type>::cast': none of the 3 overloads could convert all the argument types
        with
        [
            type=leveldb::SequentialFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(904): note: could be 'pybind11::handle pybind11::detail::type_caster_base<type>::cast(const leveldb::SequentialFile *,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::SequentialFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(876): note: or       'pybind11::handle pybind11::detail::type_caster_base<type>::cast(leveldb::SequentialFile &&,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::SequentialFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(870): note: or       'pybind11::handle pybind11::detail::type_caster_base<type>::cast(const leveldb::SequentialFile &,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::SequentialFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1838): note: while trying to match the argument list '(leveldb::SequentialFile **, pybind11::return_value_policy, nullptr)'
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2045): note: see reference to function template instantiation 'pybind11::tuple pybind11::make_tuple<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::SequentialFile**&>(const std::string &,leveldb::SequentialFile **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2199): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference>::simple_collector<const std::string&,leveldb::SequentialFile**&>(const std::string &,leveldb::SequentialFile **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2199): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference>::simple_collector<const std::string&,leveldb::SequentialFile**&>(const std::string &,leveldb::SequentialFile **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2219): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference> pybind11::detail::collect_arguments<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::SequentialFile**&,void>(const std::string &,leveldb::SequentialFile **&)' being compiled
./leveldb/leveldb.cpp(185): note: see reference to function template instantiation 'pybind11::object pybind11::detail::object_api<pybind11::handle>::operator ()<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::SequentialFile**&>(const std::string &,leveldb::SequentialFile **&) const' being compiled
./leveldb/leveldb.cpp(185): note: see reference to function template instantiation 'pybind11::object pybind11::detail::object_api<pybind11::handle>::operator ()<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::SequentialFile**&>(const std::string &,leveldb::SequentialFile **&) const' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1836): error C2665: 'pybind11::detail::type_caster_base<type>::cast': none of the 3 overloads could convert all the argument types
        with
        [
            type=leveldb::RandomAccessFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(904): note: could be 'pybind11::handle pybind11::detail::type_caster_base<type>::cast(const leveldb::RandomAccessFile *,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::RandomAccessFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(876): note: or       'pybind11::handle pybind11::detail::type_caster_base<type>::cast(leveldb::RandomAccessFile &&,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::RandomAccessFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(870): note: or       'pybind11::handle pybind11::detail::type_caster_base<type>::cast(const leveldb::RandomAccessFile &,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::RandomAccessFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1838): note: while trying to match the argument list '(leveldb::RandomAccessFile **, pybind11::return_value_policy, nullptr)'
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2045): note: see reference to function template instantiation 'pybind11::tuple pybind11::make_tuple<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::RandomAccessFile**&>(const std::string &,leveldb::RandomAccessFile **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2199): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference>::simple_collector<const std::string&,leveldb::RandomAccessFile**&>(const std::string &,leveldb::RandomAccessFile **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2199): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference>::simple_collector<const std::string&,leveldb::RandomAccessFile**&>(const std::string &,leveldb::RandomAccessFile **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2219): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference> pybind11::detail::collect_arguments<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::RandomAccessFile**&,void>(const std::string &,leveldb::RandomAccessFile **&)' being compiled
./leveldb/leveldb.cpp(196): note: see reference to function template instantiation 'pybind11::object pybind11::detail::object_api<pybind11::handle>::operator ()<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::RandomAccessFile**&>(const std::string &,leveldb::RandomAccessFile **&) const' being compiled
./leveldb/leveldb.cpp(196): note: see reference to function template instantiation 'pybind11::object pybind11::detail::object_api<pybind11::handle>::operator ()<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::RandomAccessFile**&>(const std::string &,leveldb::RandomAccessFile **&) const' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1836): error C2665: 'pybind11::detail::type_caster_base<type>::cast': none of the 3 overloads could convert all the argument types
        with
        [
            type=leveldb::WritableFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(904): note: could be 'pybind11::handle pybind11::detail::type_caster_base<type>::cast(const leveldb::WritableFile *,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::WritableFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(876): note: or       'pybind11::handle pybind11::detail::type_caster_base<type>::cast(leveldb::WritableFile &&,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::WritableFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(870): note: or       'pybind11::handle pybind11::detail::type_caster_base<type>::cast(const leveldb::WritableFile &,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::WritableFile
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1838): note: while trying to match the argument list '(leveldb::WritableFile **, pybind11::return_value_policy, nullptr)'
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2045): note: see reference to function template instantiation 'pybind11::tuple pybind11::make_tuple<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::WritableFile**&>(const std::string &,leveldb::WritableFile **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2199): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference>::simple_collector<const std::string&,leveldb::WritableFile**&>(const std::string &,leveldb::WritableFile **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2199): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference>::simple_collector<const std::string&,leveldb::WritableFile**&>(const std::string &,leveldb::WritableFile **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2219): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference> pybind11::detail::collect_arguments<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::WritableFile**&,void>(const std::string &,leveldb::WritableFile **&)' being compiled
./leveldb/leveldb.cpp(207): note: see reference to function template instantiation 'pybind11::object pybind11::detail::object_api<pybind11::handle>::operator ()<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::WritableFile**&>(const std::string &,leveldb::WritableFile **&) const' being compiled
./leveldb/leveldb.cpp(207): note: see reference to function template instantiation 'pybind11::object pybind11::detail::object_api<pybind11::handle>::operator ()<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::WritableFile**&>(const std::string &,leveldb::WritableFile **&) const' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1836): error C2665: 'pybind11::detail::type_caster_base<type>::cast': none of the 3 overloads could convert all the argument types
        with
        [
            type=leveldb::FileLock
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(904): note: could be 'pybind11::handle pybind11::detail::type_caster_base<type>::cast(const leveldb::FileLock *,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::FileLock
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(876): note: or       'pybind11::handle pybind11::detail::type_caster_base<type>::cast(leveldb::FileLock &&,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::FileLock
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(870): note: or       'pybind11::handle pybind11::detail::type_caster_base<type>::cast(const leveldb::FileLock &,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::FileLock
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1838): note: while trying to match the argument list '(leveldb::FileLock **, pybind11::return_value_policy, nullptr)'
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2045): note: see reference to function template instantiation 'pybind11::tuple pybind11::make_tuple<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::FileLock**&>(const std::string &,leveldb::FileLock **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2199): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference>::simple_collector<const std::string&,leveldb::FileLock**&>(const std::string &,leveldb::FileLock **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2199): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference>::simple_collector<const std::string&,leveldb::FileLock**&>(const std::string &,leveldb::FileLock **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2219): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference> pybind11::detail::collect_arguments<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::FileLock**&,void>(const std::string &,leveldb::FileLock **&)' being compiled
./leveldb/leveldb.cpp(305): note: see reference to function template instantiation 'pybind11::object pybind11::detail::object_api<pybind11::handle>::operator ()<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::FileLock**&>(const std::string &,leveldb::FileLock **&) const' being compiled
./leveldb/leveldb.cpp(305): note: see reference to function template instantiation 'pybind11::object pybind11::detail::object_api<pybind11::handle>::operator ()<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::FileLock**&>(const std::string &,leveldb::FileLock **&) const' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1836): error C2665: 'pybind11::detail::type_caster_base<type>::cast': none of the 3 overloads could convert all the argument types
        with
        [
            type=leveldb::Logger
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(904): note: could be 'pybind11::handle pybind11::detail::type_caster_base<type>::cast(const leveldb::Logger *,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::Logger
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(876): note: or       'pybind11::handle pybind11::detail::type_caster_base<type>::cast(leveldb::Logger &&,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::Logger
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(870): note: or       'pybind11::handle pybind11::detail::type_caster_base<type>::cast(const leveldb::Logger &,pybind11::return_value_policy,pybind11::handle)'
        with
        [
            type=leveldb::Logger
        ]
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(1838): note: while trying to match the argument list '(leveldb::Logger **, pybind11::return_value_policy, nullptr)'
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2045): note: see reference to function template instantiation 'pybind11::tuple pybind11::make_tuple<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::Logger**&>(const std::string &,leveldb::Logger **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2199): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference>::simple_collector<const std::string&,leveldb::Logger**&>(const std::string &,leveldb::Logger **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2199): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference>::simple_collector<const std::string&,leveldb::Logger**&>(const std::string &,leveldb::Logger **&)' being compiled
D:\python-leveldb\third_party\pybind11\include\pybind11\cast.h(2219): note: see reference to function template instantiation 'pybind11::detail::simple_collector<pybind11::return_value_policy::automatic_reference> pybind11::detail::collect_arguments<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::Logger**&,void>(const std::string &,leveldb::Logger **&)' being compiled
./leveldb/leveldb.cpp(350): note: see reference to function template instantiation 'pybind11::object pybind11::detail::object_api<pybind11::handle>::operator ()<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::Logger**&>(const std::string &,leveldb::Logger **&) const' being compiled
./leveldb/leveldb.cpp(350): note: see reference to function template instantiation 'pybind11::object pybind11::detail::object_api<pybind11::handle>::operator ()<pybind11::return_value_policy::automatic_reference,const std::string&,leveldb::Logger**&>(const std::string &,leveldb::Logger **&) const' being compiled

It seems it is erroring due to c++ ** args

[YannickJadoul]

Yes. pybind11 does not support pointers to pointers to something. What type would you expect that to be on the Python side?

[kumaraditya303]

Yes. pybind11 does not support pointers to pointers to something. What type would you expect that to be on the Python side?

@YannickJadoul I would expect a class instance on the python side. Also is there any temporary workaround for that?

[YannickJadoul]

No, but ... why would you have a pointer to a pointer to a class just give you a class? That doesn't really make sense.

A workaround, yes: just accept an object of a class by value, reference, or pointer, and pass it on to the function that's expecting a pointer to pointer.

[EricCousineau-TRI]

One minor pain point I've ran into is wrapping calls to PYBIND11_OVERRIDE* macros.

We've worked around in Drake, but it ain't pretty. Example (older fork of pybind11, so you'll need to munge the names):
https://github.com/RobotLocomotion/drake/blob/6ee5e9325821277a62bd5cd5456ccf02ca25dab7/bindings/pydrake/systems/framework_py_systems.cc#L110-L159

[kumaraditya303]

@YannickJadoul If I accept an object then the methods signature is changed hence I cannot override the method in the trampoline class. This is what I did:

  Status NewLogger(const std::string &fname, Logger *result) override {
    PYBIND11_OVERRIDE_PURE(
        Status,    /* Return type */
        Env,       /* Parent class */
        NewLogger, /* Name of function in C++ (must match Python name) */
        fname, result);
  }

Error while compiling:

./leveldb/leveldb.cpp(233): error C3668: 'PyEnv::NewLogger': method with override specifier 'override' did not 
override any base class methods

It would be helpful if you could provide a snippet for the method, for better clarification.
Trampoline class is for Env class of https://github.com/google/leveldb/blob/master/include/leveldb/env.h

[YannickJadoul]

@kumaraditya303, right, so you'll have to wrap that function in the trampoline class and forward calls to the actual hierarchy, somehow, and you probably can't use PYBIND11_OVERRIDE_PURE, as @EricCousineau-TRI indicates.

But again, Foo ** cannot be converted to a valid Python type, as ... well, it has properties you can't match with Python object. As an argument, you can't change the object a variable reference, for example, in Python.