Using C++ Classes From D: dmd cannot link, while ldc segfault

[mw via Digitalmars-d-learn]

Hi,

I'm following this example:
https://dlang.org/spec/cpp_interface.html#using_cpp_classes_from_d

and try to wrap a std::list

base.cpp
```cpp
#include <iostream>
#include <list>

using namespace std;

class Base
{
    public:
        virtual void print3i(int a, int b, int c) = 0;
};

class Derived : public Base
{
    public:
        int field;
        Derived(int field) : field(field) {}

        void print3i(int a, int b, int c)
        {
            cout << "a = " << a << endl;
            cout << "b = " << b << endl;
            cout << "c = " << c << endl;
        }

        int mul(int factor);
};

template<class T> class std_list : public std::list<T> {};
void getInts(std_list<int>* list);

int Derived::mul(int factor)
{
    return field * factor;
}

Derived *createInstance(int i)
{
    // get list of ints from D side
    std_list<int> list;
    list.push_back(911);
    ::getInts(&list);
    for (int i : list) {
            cout << "i = " << i << endl;
    }

    return new Derived(i);
}

void deleteInstance(Derived *&d)
{
    delete d;
    d = 0;
}
```

main.c
```
extern(C++)
{
    abstract class Base
    {
        void print3i(int a, int b, int c);
    }

    class Derived : Base
    {
        int field;
        @disable this();
        override void print3i(int a, int b, int c);
        final int mul(int factor);
    }

    Derived createInstance(int i);
    void deleteInstance(ref Derived d);
}

extern(C++) {

class std_list(T) {
  @disable this();
  void push_back(const ref T value);
}

void getInts(std_list!(int) list) {
  foreach (int i; 0 .. 10) {
    list.push_back(i);
  }
}

}

void main()
{
    import std.stdio;

    auto d1 = createInstance(5);
    writeln(d1.field);
    writeln(d1.mul(4));

    Base b1 = d1;
    b1.print3i(1, 2, 3);

    deleteInstance(d1);
    assert(d1 is null);

    auto d2 = createInstance(42);
    writeln(d2.field);

    deleteInstance(d2);
    assert(d2 is null);
}

```

Makefile
```
c2d:
        g++ -c -g -ggdb base.cpp
        ldmd2 -g main.d base.o -L-lstdc++ && ./main

```

if I use LCD (ldmd2), it segfaults:
```
$ make
g++ -c -g -ggdb base.cpp
ldmd2 -g main.d base.o -L-lstdc++ && ./main
Segmentation fault (core dumped)
```

and gdb shows it fails at: main.d:29 list.push_back(i);

if I use DMD, it cannot link:
```
$ make
g++ -c -g -ggdb base.cpp
dmd -g main.d base.o -L-lstdc++ && ./main
/usr/bin/ld: main.o:(.data._D4main__T8std_listTiZQm6__vtblZ+0x0): 
undefined reference to `std_list<int>::push_back(int const&)'
collect2: error: ld returned 1 exit status
Error: linker exited with status 1
```

Looks like something wrong with the push_back().

So, how to fix this DMD link error, and LDC segfaults?

Thanks.