To help LDC/GDC

[Manu]

On 9 April 2013 14:39, Walter Bright <newshound2 at digitalmars.com> wrote:

> On 4/8/2013 5:37 AM, Manu wrote:
>
>>     Only builtins are pure in the sense of 'C'.  Even functions considered
>>     PUREstrong by the frontend may update an internal state, so the rules
>> just
>>     don't apply.  Except for maybe global functions...   In any case, the
>> only
>>     benefit you can reap from 'D pure' functions are that they are more
>> likely
>>     to be const-folded / inlined.
>>
>> Oh my god... ..... this is the most upsetting thing I've heard all day! :(
>> No really, I have been SOOOO excited for so long about this optimisation
>> potential in D!
>> There's gotta be something that can be done! >_<
>>
>
> I believe Iain is incorrect. Pure functions cannot squirrel away any
> persistent state.
>

Are you saying the example above is not actually valid code?

struct Foo {
    int a = 0;
    pure int bar( int n ) { // Weakly pure
        a += n;
        return a;
    }
}

That's not pure. Call it twice with the same args, you'll different
answers. How can that possibly be considered pure in any sense?
And it's useless in terms of optimisation, so why bother at all? What does
it offer?
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