[racket] empty hash tables

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On 05/30/11 15:00, Matthew Flatt wrote:
> How would `hash-empty?' be different than `hash-count' for a weak hash
> table? A traversal of the table is needed to check whether any keys
> have disappeared.

But as soon as an non-disappeared key has been found `hash-empty?' could
return without needing to traverse the rest of the table.

> That is, I don't see how to make `hash-empty?' on a
> weak table a constant-time operation without additional GC support.

It might not be possible to make `hash-empty?' a constant-time
operation, but in a big table the difference between traversing until
the first non-disappeared key and traversing the complete table would
still be significant, wouldn't it?

Marijn

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