TempAlloc review starts now

[Steven Schveighoffer]

On Sun, 05 Jun 2011 18:25:07 -0400, Lars T. Kyllingstad  
<public at kyllingen.nospamnet> wrote:

> All right, folks, it's time to get the review queue started again.  First
> up is David Simcha's TempAlloc, which, if accepted, is to be included in
> the core.memory module in druntime.

newVoid: I don't really like the name of this -- void is a type.  It  
suggests you are allocating a new void array.  I'm not sure we should  
adopt the hacky syntax that D uses to say "don't initialize" as a symbol  
name.

Particularly, this looks odd:

newVoid!double

What the hell does that mean? :)

I suggest a name like newUninit or newRaw or something that means more  
"uninitailized" than "no type".

alignedMalloc:

I seriously question having such a feature.  According to my C++ book  
malloc returns a pointer "suitably aligned for any type".  According to  
Microsoft, malloc is 16-byte aligned (of course, D doesn't use microsoft's  
runtime, DMC doesn't seem to identify alignment in malloc docs).  GNU  
appears to guarantee 8-byte alignment on 32-bit systems, 16 on 64-bit  
systems (making this function mostly useless on 64-bit dmd).

There are also some posix functions that align a malloc to a requested  
size (see memalign).

At the very least, the function should identify what the alignment is if  
you *don't* use it.  I'd like to see a good use case for this feature in  
an example, otherwise, I think it should be killed.

That being said, wrapping malloc might have some nice other features too.   
I like the auto-adding of the range to the GC.

tempdup:

1. If this uses ElemType!(R)[] as the return type, duping a char[] will  
give you a dchar[].  I don't think this is very desirable.
2. What happens for something like immutable(uint *)[]?  Does it become  
uint *[]?  Because that would be bad...

TempAlloc.malloc:

I don't like void * as a return value.  Would it not be more appropriate  
to use at least void[]?  I'd suggest actually for malloc to take a  
template parameter of the type to return, defaulting to void.  i.e.:

T[] malloc(T = void)(size_t size);

auto x = TempAlloc.malloc(50); // allocate a void[] of size 50
auto x = TempAlloc.malloc!int(50); // allocate an int[] of size 50 ints.

Same should go to alignedMalloc if that feature stays.

-Steve