On 29/12/2012 21:13, Peter Alexander wrote:
On Saturday, 29 December 2012 at 20:59:56 UTC, Stewart Gordon wrote:
<snip>
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.
Yes, you have a point there. Any facility for creating a range by
combining ranges is liable to overflow if it defines a length property.
But I would expect that in practice 99% of finite ranges would be
nowhere near 2^64 in size, so an overflow would be an exceptional case.
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.
Maybe the solution is to define two permutation range classes: one with
length that asserts that the number of elements <= 20, and one without
length that places no bound.
If the set size is a template parameter rather than being set at run
time, then it can define length conditionally.
Stewart.
