Re: std.reflection prototype

[bitwise via Digitalmars-d]

On Wed, 15 Apr 2015 15:48:28 -0400, Jacob Carlborg <d...@me.com> wrote:
On 2015-04-15 17:26, bitwise wrote:

Right now, this is the def:

/**
  * Array of pairs giving the offset and type information for each
  * member in an aggregate.
  */
struct OffsetTypeInfo
{
     size_t   offset;    /// Offset of member from start of object
     TypeInfo ti;        /// TypeInfo for this member
}

If "string name" esd added, and then offTi[] esd actually populated,
then I suppose you could do this:

class Test {
     int a = 4;
     private int b = 5;
     void print(){ writeln(b); }
}

void main()
{
     Test test = new Test;
     // offsetof would instead come from the TypeInfo/OffsetTypeInfo
     int* b = cast(int*)(cast(void*)test + Test.b.offsetof);
     *b = 1234;
     test.print();
}

But AFAIK, this is NOT ok in C++ because of the way inheritance works..
is this safe in D?

I'm not sure, I would assume so. Why is this not safe in C++?


One reason is that casting with multiple inheritance offsets the pointer,  
and I forget exactly virtual inheritance works, but I'm sure it breaks  
things too..

#include <iostream>
using namespace std;

class A {
    public: int a;
};

class B {
    public: int b;
};

class C {
    public: int c;
};

class D : public A, public B, public C {
    public: int d;
};

int main(int argc, const char * argv[])
{
    D *d = new D;

    cout << (intptr_t)d << endl;
    cout << (intptr_t)(C*)d << endl;
    cout << (intptr_t)(B*)d << endl;
    cout << (intptr_t)(A*)d << endl;
    return 0;
}

possible output:

1098416
1098424
1098420
1098416