Re: [Haskell-cafe] ANN: unordered-containers - a new, faster hashing-based containers library

* Max Bolingbroke [2011-02-21 14:57:08+0000]

On 20 February 2011 03:40, Louis Wasserman wrote:

...

I'd like to complain about that, too ;)

I'm curious, when do people find that they need a really fast way to get map size? I use them quite a lot, and almost never call length - and when I do, it is typically only to get some statistics about the map for user display - certainly not in an inner loop.

I find it is still useful to have a way to quickly test if a map is empty (for e.g. fixed points that slowly grow a map by unioning in a new bit every time) but "null" works OK for that purpose.

For example, consider a situation where you have two sets (they can be maps as well), 'a' and 'b', such that by construction you know that 'a' is a subset (submap) of 'b'. Now, size a < size b is a convenient O(1) way to test whether 'a' is a proper subset (submap) of 'b'. -- Roman I. Cheplyaka :: http://ro-che.info/ Don't worry what people think, they don't do it very often.