How do "pure" member functions work?

[Timon Gehr]

On 08/21/2011 09:10 PM, Don wrote:
> bearophile wrote:
>> Sean Eskapp:
>>
>>> Oh, I see, thanks! This isn't documented in the function documentation!
>>
>> D purity implementation looks like a simple thing, but it's not
>> simple, it has several parts that in the last months have be added to
>> the language and compiler, and we are not done yet, there are few more
>> things to add (like implicit conversion to immutable of the results of
>> strongly pure functions). It will need several book pages to document
>> all such necessary design details.
>>
>> Bye,
>> bearophile
>
> It is actually very simple: a function marked as 'pure' is not allowed
> to explicitly access any static variables.
> Everything else is just compiler optimisation, and the programmer
> shouldn't need to worry about it.

It can be of value to know that a function is pure as in mathematics if 
it is strongly pure, but can have restricted side-effects if it is 
weakly pure.