On 05/29/2013 06:54 PM, Peter Williams wrote:
> On 30/05/13 10:49, Peter Williams wrote:
>> On 30/05/13 09:45, Ali Çehreli wrote:
>>> http://dlang.org/d-array-article.html
> Thinking about this some more, it seems I still need the const even with
> pass by value to reassure the caller that his array won't be altered. So
> the problem doesn't go away it just changes slightly.
It is sensible that the parameter be const-element, non-const-slice:
void foo(const(int)[] arr);
> I find the mechanism described in the article a little disconcerting and
> it certainly needs more publicity as it's a bug in waiting for the
> unwary.
It certainly is disconcerting. Performance have played a big role in the
current semantics of slices.
> Wouldn't a better rule for pass by value be that any changes to
> the data part of the array (including assignment to an element) causes
> reallocation of the entire data portion.
The type of a slice parameter is not different than a local slice
variable. Since we wouldn't want an entire copy of the elements due to
an element mutation:
int[] whole = // ...;
int[] firstHalf = whole[0 .. $/2];
firstHalf = 42; // this should affect whole
Moving the last two lines to a new function should not change meaning:
int[] whole = // ...;
setFirstHalf(whole, 42); // should still affect whole
Ali
