How to remove all items in an associative array?

[Bill Baxter]

Oskar Linde wrote:
> Bill Baxter wrote:
>> Yang Bo wrote:
>>> http://www.digitalmars.com/d/statement.html said:
>>>
>>> The aggregate must be loop invariant, meaning that elements to the
>>> aggregate cannot be added or removed from it in the
>>> NoScopeNonEmptyStatement.
>>>
>>> So, how can I remove them?
>> I don't understand the body, but the answer to the question in the
>> subject line is   AA = null;  or  AA = AA.init;
> 
> Since quite a while ago, the D associative arrays have become pure
> reference types. While the above has the apparent effect of clearing the
> array, it does in fact just reassign the current reference. If you have
> several references to the same associative array, the above will not
> clear the actual array referred to.
> 
> To clear the actual array, you need to resort to hackery.  Something
> like this should definitely be included in the compiler/runtime.
> 
> private struct BB { void*[]b; size_t nodes; }
> 
> private union ToPtr(T) {T x; void * ptr; }
> 
> void clear(T,E)(T[E] aa) {
>     ToPtr!(typeof(aa)) toptr;
>     toptr.x = aa;
>     BB* b = cast(BB*) toptr.ptr;
>     if (b) {
>         b.b = null;
>         b.nodes = 0;
>     }
> }
> 
>> http://www.prowiki.org/wiki4d/wiki.cgi?DocComments/Arrays
> 
> I rewrote that section in a way that hopefully explains the semantics
> better.
> 
> This question comes up frequently enough to merit an addition to the
> official documentation and a clear/deleteAll implementation (like the
> one above) should definitely be added to the language and
> phobos/internal/aaA.d.

Interesting tidbit.  Thanks for the info and for updating that page.

--bb