GC for pure functions -- implementation ideas

[dsimcha]

On 4/15/2011 5:01 PM, Sean Kelly wrote:
> On Apr 15, 2011, at 1:12 PM, Don wrote:
>>
>> Create a pure heap for each thread. This is a heap which can only be
>> used by pure functions. I present some simplistic code, with the
>> simplest possible implementation: just a big block of memory with a thread local 'stack pointer' which points to the first free slot.
>
> It's a good idea.  dsimcha was already going to polish his TempAlloc, wasn't he?  Seems like this is nearly the same thing.

Yeah, I never formalized it at all, but that's roughly what TempAlloc 
accomplishes.  My other concern is, what happens in the case of the 
following code:

uint nonLeaky() pure {
     foreach(i; 0..42) {
          auto arr = new uint[666];
          // do stuff
     }

     return 8675309;
}

In this case the arr instance from every loop iteration is retained 
until nonLeaky() returns, whether it's referenced or not.  Granted, this 
is a silly example, but I imagine there are cases where stuff like this 
happens in practice.