Safely moving structs in D

[sarn via Digitalmars-d-learn]

On Monday, 23 January 2017 at 22:26:58 UTC, bitwise wrote:
> Is it ok to memcpy/memmove a struct in D?
>
> Quote from here:
> https://dlang.org/spec/garbage.html
>
> "Do not have pointers in a struct instance that point back to 
> the same instance. The trouble with this is if the instance 
> gets moved in memory, the pointer will point back to where it 
> came from, with likely disastrous results."
>
> This seems to suggests it's ok to move structs around in memory 
> without calling their postblit...but if this is the case, why 
> does postblit even exist, if it's not strictly guaranteed to be 
> called after the struct has been blitted?

You may need the postblit for a *copying* blit.  For example, if 
a struct does reference counting, the postblit will need to 
increment the count for the new copy.  It's a slightly different 
solution to what C++ solves with copy constructors, assignment 
operators, etc.  Compared to C++, the D approach is a bit simpler 
and trades off a little flexibility for more opportunities for 
the compiler to generate efficient code.

Here's the situation in C++, BTW:
http://en.cppreference.com/w/cpp/language/rule_of_three