On Mon, 19 May 2014 23:14:03 -0400, Jonathan M Davis via Digitalmars-d
<digitalmars-d@puremagic.com> wrote:
On Mon, 19 May 2014 13:11:43 -0400
Steven Schveighoffer via Digitalmars-d <digitalmars-d@puremagic.com>
wrote:
On Mon, 19 May 2014 12:35:26 -0400, Jonathan M Davis via
Digitalmars-d <digitalmars-d@puremagic.com> wrote:
> On Mon, 19 May 2014 09:42:31 -0400
> Steven Schveighoffer via Digitalmars-d <digitalmars-d@puremagic.com>
> wrote:
>
>> On Sun, 18 May 2014 09:58:25 -0400, H. S. Teoh via Digitalmars-d
>> <digitalmars-d@puremagic.com> wrote:
>>
>> > On Sat, May 17, 2014 at 11:51:44AM -0700, Jonathan M Davis via
>> > Digitalmars-d wrote:
>> >> On Thu, 15 May 2014 08:43:11 -0700
>> >> Andrei Alexandrescu via Digitalmars-d
>> >> <digitalmars-d@puremagic.com> wrote:
>> >>
>> >> > On 5/15/14, 6:28 AM, Dicebot wrote:
>> >> > > This is not true. Because of such code you can't ever
>> >> > > automatically memoize strongly pure function results by
>> >> > > compiler. A very practical concern.
>> >> >
>> >> > I think code that doesn't return pointers should be
>> >> > memoizable. Playing tricks with pointer comparisons would be
>> >> > appropriately penalized. -- Andrei
>> >>
>> >> Agreed. The fact that a pure function can return newly allocated
>> >> memory pretty much kills the idea of being able to memoize pure
>> >> functions that return pointers or references, because the
>> >> program's behavior would change if it were to memoize the
>> >> result and reuse it.
>>
>> Memoizing reference returns that are immutable should be fine.
>
> Only if you consider it okay for the behavior of the function to
> change upon
> memoization - or at least don't consider that the behaviors changed
> due to the
> fact that the objects are equal but not the same object (which can
> matter for
> reference types)
It shouldn't matter. Something that returns immutable references,
can return that same thing again if asked the same way.
Except that a pure function _can't_ return the same object by definition
- not
unless it was passed in via an argument.
Compiles today (2.065):
immutable(Object) alloc() pure
{
static immutable o = new immutable(Object);
return o;
}
Such a program is incorrectly written.
Well, then Object.toHash is incorrectly written.
It might actually be, yes. toHash really should examine the object
contents, not the address.
-Steve
