Uh... destructors?

[Steven Schveighoffer]

On Tue, 22 Feb 2011 16:34:21 -0500, bearophile <bearophileHUGS at lycos.com>  
wrote:

> Steven Schveighoffer:
>
>> Freeing and allocating memory is fair game for pure functions.
>
> Allocating arrays and objects is possible in pure D functions, despite  
> the memory pointers they contain (like the ptr of a returned array) are  
> different across different calls. This makes those function only  
> formally pure and requires care from both the programmer and the  
> optimizations done by the compiler, to avoid some bad bugs :-)
>
> Example: the C calloc() function is not considered pure, despite what it  
> does is not so far from a pure D function that allocates and returns a  
> dynamic array of ubytes:
>
> import core.stdc.stdlib: calloc;
>
> // OK
> pure ubyte* foo1(int n) {
>     auto a = new ubyte[n];
>     return a.ptr;
> }
>
> // Error: pure function 'foo2' cannot call impure function 'calloc'
> pure ubyte* foo2(int n) {
>     return cast(ubyte*)calloc(n, 1);
> }
>
> void main() {}

I would think malloc and friends should be pure, as well as free.  They  
can easily simply be marked pure, since they are C bindings.

> Regarding freeing memory in pure functions, I am even less sure.

If allocation is pure, freeing should also be pure.  You should be allowed  
to clean up what you created in a pure function.

To draw a parallel, a GC collect cycle should be "pure", even though it  
affects global state.  Otherwise, the GC would have to be disabled during  
pure functions.

-Steve