Memory allocation purity

[Walter Bright via Digitalmars-d]

On 5/15/2014 2:41 PM, Timon Gehr wrote:
> On 05/15/2014 11:33 PM, Walter Bright wrote:
>> On 5/15/2014 9:07 AM, Timon Gehr wrote:
>>> Why? A memoizable function is still memoizable if it is changed
>>> internally to
>>> memoize values in global memory, for example.
>>
>> I doubt a compiler could prove it was pure.
>>
>
> Yes, that was actually my point. Memoizable is actually a non-trivial property.
>
> (But note that while a compiler cannot in general discover a proof, it could
> just _check_ a supplied proof.)

If the compiler cannot mechanically verify purity, the notion of purity is 
rather useless, since as this thread shows it is incredibly easy for humans to 
be mistaken about it.