Re: DMD 1.038 and 2.022 releases

[Denis Koroskin]

On Tue, 16 Dec 2008 01:48:21 +0300, mastrost <titi.mas...@free.fr> wrote:

Hi,

first of all, thank you Walter and all the D community for making the great "pure"

feature become reality.
I have 2 questions concerning the behaviour of this feature.

The first one concerns the existence -or not- of "pure delegates".

It makes sense to use a delegate if its closure is not empty -otherwise it is no more than a function-. This is the reason why we can think delegates cannot be

pure. Let's take an example:

void foo(){
    int x=0;
    //bar is not pure at all in this context
    int bar(){
        return x;
    }
    writefln(bar()); // prints '0'
    ++x;
    writefln(bar()); // prints '1'
}

But the fact is that when returning a delegate, its closure freezes forever and so behaves like a local variable and not like a global variable by respect to the

delegate :

int delegate() getPureFunction(int x){
    int bar(){
        return x;
    }
    return &bar;
}

void main(){
    int delegate() myPureFunction;
    myPureFunction = getPureFunction(5);
}

In this example, myPureFunction looks like a pure function, does it?

So how does dmd 2.022 behave for such kind of "pure delegates" ? Do you think there is a futur for pure delegates in the D language ? If not this would mean that we cannot use the power of delegates (to do real functionnal programming) and

the power of purity in the same time, which will be very disapointing for
programmers, don't you think ?

Yes, it was previously discussed many times (not only delegates but any 
function in general (locally impure)).
Current plan it to make pure function restrictive and then lift unnecessary 
restrictions where possible.

This was my first question. The second one concerns purity and parallel

programming. Is dmd 2.022 implementing some kind of parallelism thanks to pure function? In fact I have been argued that "pure" keyword is not enough for the compiler to make an efficient parallel program. The problem would be that the compiler has no mean to know the granularity of the tasks. What are your feelings

about that?

This is not implemented yet. Pure function are just being added into language.

Thanks a lot