On Thu, 09 Jun 2011 16:08:33 -0400, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
On 6/9/11 12:51 PM, KennyTM~ wrote:
Given that the 'new' expression can be used in 'pure', should it be that
GC allocation functions like GC.malloc, GC.qalloc and GC.extend (?) be
weakly pure also? And should it apply to other managed allocators as
well, e.g. the proposed TempAlloc?
I'm asking this as one of the specializations of std.conv.toImpl calls
GC.malloc, which is one of the 11 causes preventing std.conv.to from
being pure, and GC.qalloc and GC.extend (and memcpy and Array.capacity)
are used by std.array.appender (of pure range), and appender is also a
major reason why std.conv.to is not pure.
GC.malloc is not technically pure because its result does not only
depend on arguments - it's a fresh value each time. So the compiler
can't apply pure reasoning to it.
It's weak-pure, not strong-pure. weak-pure functions are allowed to
return different values for two different runs with the same parameters.
Essentially, weak-pure functions cannot have pure reasoning applied to
them, *but* they can be called from strong-pure functions.
It's not technically even weak-pure because it uses global data. But
because memory allocation is so important to any functional programming,
it needs to be an exception.
-Steve
