Discussion Thread: DIP 1040--Copying, Moving, and Forwarding--Community Review Round 1

[Walter Bright]

One problem unaddressed is, for moveable structs, what if there *are* interior 
pointers, and they wind up pointing to a defunct object? The current compiler 
never moves structs, so this problem never occurs.

Some off the top of my head possibilities:

1. never move structs in @safe code (or at least disable moving structs that 
contain pointers). Unfortunately, ref counted objects must have a payload 
pointer in them.

2. add a runtime check on field pointer assignments

3. add an invariant() runtime check on field pointer values

4. insist that field pointers be marked with @system (there's another DIP for 
marking variables as @system)

P.S. the original reason for not allowing interior pointers is so a compacting 
garbage collector could be used.