ponce

[Don]

Steven Schveighoffer wrote:
> On Tue, 09 Nov 2010 17:14:33 -0500, Don <nospam at nospam.com> wrote:
> 
>> bearophile wrote:
>>> Jonathan M Davis:
>>>
>>>> it would be possible to make it so that any objects allocated with 
>>>> new during CTFE would be in the dynamic heap during runtime.
>>>  This is possible, but it doesn't seem what you usually desire when 
>>> you allocate an object at compile time.
>>>  Bye,
>>> bearophile
>>
>> If it's mutable, it'll go on the heap. If it's immutable, it could 
>> optionally go into read-only memory (it will be exactly like the .init 
>> of a class instance). Classes which are used only during execution of 
>> CTFE functions will not be instantiated at runtime.
> 
> Pardon my ignorance, but how can something evaluated at compile time go 
> on the heap?  The heap doesn't exist yet!
> 
> e.g.:
> 
> class C
> {
>   int[] buffer;
>   this() pure { buffer = new int[125];}
> }
> 
> C c = new C;
> 
> How does c go on the heap at compile time?  Won't you have to re-run the 
> constructor at runtime to get the right result?  Not only that, but even 
> if you did run the ctor at compile time, how do you make a copy of c for 
> every thread without re-running the ctor?
> 
> -Steve

The situation isn't any different to what we already have. You can 
already do:

struct F
{
    int [] w;
}

F[] foo() {
    F[] x = new F[6];
    foreach(i; 0..x.length)
       x[i].w = new int[20];
    return x;
}
and foo() can be run at compile time.

OTOH, I don't know if there is any case where a CTFE value can actually 
end up on the heap at runtime. CTFE only kicks in when you need a 
manifest constant, and AFAIK there's no way to require a class manifest 
constant -- just an element of one.