Memory allocation purity

[Manu via Digitalmars-d]

On 15 May 2014 22:30, Steven Schveighoffer via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
> On Thu, 15 May 2014 07:52:20 -0400, Manu via Digitalmars-d
> <digitalmars-d at puremagic.com> wrote:
>
>> On 15 May 2014 10:50, Walter Bright via Digitalmars-d
>> <digitalmars-d at puremagic.com> wrote:
>>>
>>> On 5/14/2014 5:03 PM, Meta wrote:
>>>>
>>>>
>>>> Allocating memory through new and malloc should always be pure, I think,
>>>> because
>>>> failure either returns null in malloc's case,
>>>
>>>
>>>
>>> malloc cannot be pure if, with the same arguments, it returns null
>>> sometimes
>>> and not other times.
>>
>>
>> Even if it doesn't fail, malloc called with identical arguments still
>> returns a different result every time.
>> You can't factor malloc outside a loop and cache the result because
>> it's being called repeatedly with the same argument like you're
>> supposed to be able to do with any other pure function.
>> You shouldn't be able to do that with gcalloc either... how can gcalloc be
>> pure?
>
>
> That only applies to strong-pure functions. malloc would be weak-pure, since
> it returns a mutable pointer.

Why should returning a mutable pointer imply weak purity?