minimal object.d implementation that allows classes

[Jean-Louis Leroy]

On Thursday, 7 December 2017 at 13:08:09 UTC, Luís Marques wrote:
> On Thursday, 7 December 2017 at 08:59:08 UTC, Wild wrote:
>> You could modify the one I use for PowerNex[1]. It is a hacked 
>> version of Adam D. Ruppes
>> minimal.zip. There are only a few imports for strlen, 
>> mem{set,move,cpy}, etc.
>
> This one seems to be the one for me. For instance, 
> typeid(ClassName) seems to work, which I need.
>
> For completeness, I had looked into minlibd but it didn't 
> seemed compatible with LDC and difficult for me to fix, IIRC. 
> Regarding Mike's question of what my use case is, I wanted my 
> program to run in webassembly/asmjs. Since druntime/phobos 
> haven't been ported to that target, I was being careful with my 
> design to not depend on the runtime, but then I found out I 
> love the openmethods package. So I decided to check if I could 
> implement just enough of druntime to allow a forked version of 
> openmethods to work. As far as I can  tell that's feasible.

I am currently trying to understand how the compiler and the 
runtime interact. ClassInfo contains a vtbl array whose ptr 
property is the same as the vptr found in an instance of that 
class. However, when I modify that pointer (e.g. by reserving 
1000 more entries) and create a new instance, it still contains 
the old pointer. So it looks like the compiler sets the vptr 
without consulting the ClassInfo but somehow reflects it there. 
I'd appreciate if anybody can explain how it works, or sends me 
links to relevant info.

Example:

import std.stdio;

class Foo {
   void foo() {}
}

void main() {
   auto oldPtr = Foo.classinfo.vtbl.ptr;
   Foo.classinfo.vtbl.reserve(1000);
   writeln(oldPtr != Foo.classinfo.vtbl.ptr); // true
   Object foo = new Foo();
   writeln(oldPtr == *cast(void***)foo); // true, alas
}

...at least that's what I get with dmd.