D's New GC and Object Allocation Pools

[Mike via Digitalmars-d]

On Sunday, 26 October 2014 at 23:20:21 UTC, Mike wrote:
> Language support for this kind of thing would be nice. `@weak` 
> attribute[1] perhaps, or `virtual`/`final` module methods 
> anyone? `final` by default please. :)
>
> [1] - 
> https://gcc.gnu.org/onlinedocs/gcc-4.9.1/gcc/Function-Attributes.html#Function-Attributes

This is turning into a fun little exploration.  After reading 
this issue [1], I discovered that DMD already compiles all the 
runtime hooks as weak references, so you only need to declare a 
new `_d_newclass` implementation anywhere in your source code to 
override `new`.

version(DigitalMars)
{
     extern (C) Object _d_newclass(const ClassInfo ci)
     {
         // add your own `new` implementation here
     }
}

void main(string[] args)
{ }

Compile with:
dmd test.d

No special compiler/linker flags or symbol names. Cool!

LDC has support for decorating functions with LLVM attributes [2] 
that could potentially include creating `weak` symbols, but LDC 
will have to decorate `_d_newclass` this way in druntime before 
overriding with this technique will be possible.

GDC also has infrastructure for supporting such attributes [3], 
but the `weak` attribute will have to be added to the list, and 
decorations added to `_d_newclass` in the same way.

Maybe I'll submit some pull requests and see how they're received.

I still don't know how to call the default implementation, using 
this technique, without copying the source code from druntime.  
That's not a deal-breaker, but it stinks.

The only way I was able to override `destroy` was to copy the 
entire object.di from druntime to my project folder and modify 
the code there.  That also stinks.

This little skirmish has opened up a few possibilities for my 
work.  Very interesting.

Mike

[1] - https://github.com/ldc-developers/ldc/issues/405
[2] - 
https://github.com/redstar/ldc/commit/69f231f48f355b6399d67950f057bea72f0a64c3
[3] - http://wiki.dlang.org/GDC/Using_GDC#Attributes