returning D string from C++?

[bitwise via Digitalmars-d-learn]

I have a Windows native window class in C++, and I need a 
function to return the window title.

So in D, I have this:
// isn't D's ABI stable enough to just return this from C++
// and call it a string in the extern(C++) interface? anyways..
struct DString
{
    size_t length;
    immutable(char)* ptr;
    string toString() { return ptr[0..length]; }
    alias toString this;
}

extern(C++) interface NativeWindow {
    DString getTitle() const;
}

and in C++, this:

class NativeWindow
{
public:
    struct DString {
        size_t length;
        const char* ptr;
    };

    virtual DString getTitle() const {
        DString ret;
        ret.length = GetWindowTextLength(_hwnd) + 1;
        ret.ptr = (const char*)gc_malloc(ret.length, 0xA, NULL);
        GetWindowText(_hwnd, (char*)ret.ptr, ret.length);
        return ret;
    }
};

So while it's not generally safe to _store_ pointers to D's GC 
allocated memory exclusively in C++, I've read that D's GC scans 
the stack, and getTitle() is being called from D(and so, is on 
that stack..right?). So is the string I'm returning safe from GC 
collection?

  Thanks