Memory allocation purity

[H. S. Teoh via Digitalmars-d]

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 at 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.
> However, that should have no effect on pure functions that return
> value types - even if the function took pointers or references as
> arguments or allocated memory internally. They should but perfectly
> memoizable.
[...]

	bool func(int x) /* pure? */ {
		int[] a, b;
		a = new int[x];
		b = new int[x];
		return (a.ptr < b.ptr);
	}

Where do you draw the line?


T

-- 
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