On Saturday, 29 December 2012 at 20:59:56 UTC, Stewart Gordon
wrote:
On 29/12/2012 01:18, Peter Alexander wrote:
My question now is what to do with really large ranges? For
example, if
we have a range of permutations of the elements in a set, when
the set
is larger than 21 the number of permutations is 21 factorial,
which is
over 2^64. As far as I see, there are three options:
They look like four to me.
It's also three, for large values of three :-)
If we define a length that may overflow, then sooner or later
some code will be called on it that calls hasLength on the
range, finds it to be true, and then relies on length and
malfunctions because the value returned doesn't match the
actual length.
Using this logic, chain shouldn't have length either (it can
overflow, as I demonstrated in the original post), but it does,
and it should. There are many ranges in Phobos that may overflow
in length.
The problem with permutations is that, for the kinds of
permutations you are likely to use often, length will not
overflow. It would be really useful to have length available when
this is the case.
