On 2009-02-27 04:43:46 -0500, bearophile <bearophileh...@lycos.com> said:
D2 supports the interval syntax in the foreach:
foreach (i; 1..1000) {...}
Such intervals are useful in a very large number of situations. So,
with the new Range support, it may be useful to allow the interval
syntax to be used in other contexts as well.
So x..y may become a first-class lazy interval from x to y-1, that can
be passed to functions too, etc, and not just used into foreach (the
compiler can recognize it, and often optimize it away in many
situations, replacing it with a normal for() loop).
I agree that having first-class intervals in the language would make it
better, especially when you want to pass intervals as function
arguments.
In the D/Objective-C bridge, I've defined the NSRange struct (a Cocoa
type representing an integer interval) so it can be created by typing
NSRange[start..end] in adition to the traditional NSMakeRange(start,
length). It's better than nothing, but even better would be the ability
to omit NSRange[] entirely.
1) x..y..s
where s is a step/stride, so you can define odd numbers, etc.
1..10..3 ==> 1 4 7
10..1..-2 ==> 10 8 6 4 2
1..5..1 ==> 1 2 3 4
I don't like this syntax much, but I think it's acceptable.
May I propose that strides not be part of the interval syntax. Keep the
interval simple (x..y) then define operators to transform them. Perhaps
the modulus operator could create a steped interval (x..y % s),
although this operator doesn't seem to fit exactly right. Perhaps just
step(x..y, s) would be enough. It'd return a special struct for
iterating the interval in bigger steps.
As for strides, why not just (a..b ~ c..d) for joining two ranges and
~(x..y) for everything outside x..y ?
2) Such intervals may enjoy a fast opIn_r() method, for quick membership test:
if (a in 0..10) {...}
if (c in 'c'..'z'+1) {...}
That'd be great if you could use them in the switch statement too:
switch (a)
{
case 0..10: break;
}
The only downside is that it may confuse people who are accustomed to
the GCC extension with define an inclusive interval this way:
switch (a)
{
case 0...10: break;
}
Perhaps we could make 3 dots mean an inclusive interval (including the
second value in the interval), and 2 dots an exclusive one (excluding
the second value).
--
Michel Fortin
michel.for...@michelf.com
http://michelf.com/
