Jeremie Pelletier Wrote:
> Justin Johansson wrote:
> > Jarrett Billingsley Wrote:
> >
> >> On Sat, Oct 3, 2009 at 5:50 PM, Justin Johansson <n...@spam.com> wrote:
> >>> How does one determine the sizeof (in bytes) of an instance of a class in
> >>> D?
> >>>
> >>> .sizeof works as advertised for structs, but for reference types,
> >>> .sizeof yields the sizeof the referencing variable (effectively same as
> >>> size of a pointer)
> >>> and not the size of the underlying instance.
> >>>
> >>> I did try scanning the NG and read spec_D1.00.pdf. Perhaps I missed it
> >>> in the latter.
> >>>
> >>> btw. I was poking under the hood of std.xml and though, wow, instances of
> >>> Element
> >>> class look humongous, and so I'm interested to how exactly how humongous.
> >
> >> There's no way to get it at compile-time in D1. The best you can do is
> >> Class.classinfo.init.length.
> >>
> >> In D2, you can use __traits(classInstanceSize, Class).
> >
> >
> > Thanks Jeremie and Jarrett for answers.
> >
> > For investigative purposes (rather than adding up class member sizes in my
> > head),
> > would I get a fair answer if I copied the class data members into a struct,
> > did a struct
> > sizeof and added 4 bytes to allow for a virtual function table pointer (in
> > the class and
> > assuming the class has a VFT)?
>
> You forgot the monitor pointer of the class, so thats (size_t.sizeof *
> 2) to add to the size of the struct.
>
> I wasn't aware of the traits method either, I just made this helper
> template to simplify its syntax:
>
> template SizeOf(alias C) if(is(C == class)) {
> enum ClassSizeof = __traits(classInstanceSize, C);
> }
Okay so PODO alone is 8 bytes.
writefln( "Object: %d", Object.classinfo.init.length);
Object: 8
And we're talking 9 bytes for a simple boxed bool and 12 bytes for a simple
boxed 32-bit integer
by the looks of things.
class Foo {
bool value;
}
class Bar {
int value;
}
writefln( "Foo: %d", Foo.classinfo.init.length);
writefln( "Bar: %d", Bar.classinfo.init.length);
Foo: 9
Bar: 12
On top of that there is possibly alignment in the heap so my 9 byte Foo would
occupy 12 or 16 bytes
of address space. Would that be correct?
Thanks for answers. Justin.
