Class instance memory overhead lower than 3 words?

Nicholas Wilson iamthewilsonator at hotmail.com
Thu Jan 25 00:10:32 UTC 2018


On Wednesday, 24 January 2018 at 21:48:21 UTC, Nordlöw wrote:
> Why is the memory overhead for a class instance as high as 3 
> words (24 bytes on 64-bit systems? I find that annoyingly much 
> for my knowledge database application. I'm aware of 
> extern(C++), having one word overhead, but such 
> extern(C++)-classes cannot use all of D; I get compilation 
> errors such as
>
> node.d(99,25): Error: Internal Compiler Error: type 
> `inout(Edge)[]` can not be mapped to C++

One pointer for the vtbl, one for the monitor, not sure what the 
other one is.

C++ classes have one pointer for the vtbl at offset of -1 
size_t.sizeof

Declaring that particular method as extern(D) will fix that 
problem.


More information about the Digitalmars-d-learn mailing list