Memory allocation purity

[Timon Gehr via Digitalmars-d]

On 05/15/2014 05:24 PM, Andrei Alexandrescu wrote:
> On 5/15/14, 3:31 AM, luka8088 wrote:
>> Yeah, I read all about weak/string purity and I do understand the
>> background. I was talking about strong purity, maybe I should pointed
>> that out.
>>
>> So, to correct myself: As I understood strong purity implies
>> memoization. Am I correct?
>
> Yes, as long as you don't rely on distinguishing objects by address.
>
> Purity of allocation is frequently assumed by functional languages

Examples?

> because without it it would be difficult to get much work done.

Why?

> Then,
> most functional languages make it difficult or impossible to distinguish
> values by their address.

If it's not impossible because of lack of the concept it's not a pure 
functional language.

> In D that's easy. A D programmer needs to be
> aware of that, and I think that's fine.
>
>
> Andrei
>
>

It's not fine: The spec claims that this problem does not exist.

http://dlang.org/function.html

"... and in cases where the compiler can guarantee that a pure function 
cannot alter its arguments, it can enable full, functional purity (i.e. 
the guarantee that the function will always return the same result for 
the same arguments)"