#include <vector>

struct MyClassImpl
{
    std::vector<int> vec;
}

ref class MyClass
{
    MyClassImpl* impl;

public:
    MyClass(const int n):
    impl(new MyClassImpl)
    {
    impl->vec.resize(n, 0);
    }

    ~MyClass()
    {
    delete impl;
    }
};

// Alternativamente
struct MyOtherClassImpl
{
    std::vector<int> vec;

    MyOtherClassImpl(const int n):
    vec(n)
    {}
}

ref class MyOtherClass
{
    MyOtherClassImpl* impl;

public:
    MyOtherClass(const int n):
    impl(new MyOtherClassImpl(n))
    {
    }

    ~MyOtherClass()
    {
    delete impl;
    }
};