Int within ranges

[Steven Schveighoffer]

On Mon, 13 Jun 2011 15:44:01 -0400, nrgyzer <nrgyzer at gmail.com> wrote:

>> On Mon, 13 Jun 2011 14:52:24 -0400, nrgyzer <nrgyzer at gmail.com>
> wrote:
>> >> On Mon, 13 Jun 2011 12:15:40 -0400, nrgyzer <nrgyzer at gmail.com>
>> > wrote:
>> >> > Hi there,
>> >> >
>> >> > is there any possibility to get a sliced array from another
> array
>> >> > between two ranges like:
>> >> >
>> >> > int[uint] myArray;
>> >> > myArray[10] = 1000;
>> >> > myArray[20] = 2000;
>> >> > myArray[30] = 3000;
>> >> > myArray[40] = 4000;
>> >> > myArray[50] = 5000;
>> >> >
>> >> > int[] newArray = myArray[>= 20 .. <= 40]; // not able to do
> this
>> >> > writeln(newArray); // should print [2000, 3000, 4000]
>> >> >
>> >> > Is there any way to do this?
>> >> import dcollections.TreeMap;
>> >> auto myArray = new TreeMap!(uint, int);
>> >> myArray[10] = 1000;
>> >> myArray[20] = 2000;
>> >> myArray[30] = 3000;
>> >> myArray[40] = 4000;
>> >> myArray[50] = 5000;
>> >> // this is a little kludgy, but necessary since you require <= 40
>> >> auto c = myArray.elemAt(40);
>> >> c.popFront();
>> >> int newArray = array(myArray[20..c]);
>> >> Note two things:
>> >> 1. int[uint] is a hash, and so has no particular order.
> Therefore,
>> > there
>> >> is no guarantee of iteration order, or that a range of such a
>> > container
>> >> (if one existed) would be properly constructed with two keys.  A
>> > TreeMap,
>> >> or RedBlackTree, is sorted, and so the order is guaranteed.
>> >> 2. dcollections.TreeMap is implemented with the same collection
> as
>> >> std.container.RedBlackTree, so you could potentially do the same
>> > thing
>> >> with it.  But the dcollections.TreeMap API is more polished.
>> >> -Steve
>> >
>> > Exactly what I'm looking for, but how can I realize that it also
>> > gives me the elements when the key doesn't exists like:
>> >
>> > import std.range;
>> > import dcollections.TreeMap;
>> >
>> > auto myArray = new TreeMap!(uint, int);
>> >
>> > myArray[10] = 1000;
>> > myArray[20] = 2000;
>> > myArray[30] = 3000;
>> > myArray[45] = 4500;
>> > myArray[50] = 5000;
>> >
>> > auto c = myArray.elemAt(40);
>> > c.popFront();
>> > int[] newArray = array(myArray[20..c]);
>> > writeln(newArray);
>> >
>> > This will throw an exception because element 40 doesn't exist. Is
>> > there any possibility to get the element 20 and 30 from this map?
>> It might be useful to have elemAt return an empty range that is
> located at
>> the place the element *would* be.
>> When this code was first written, in order to detect whether elemAt
> found
>> your element, you compared it to container.end (similar to C++'s
> STL).
>> But now that cursors are tiny ranges, and have an empty property, I
> can
>> use that to indicate the element wasn't exactly found.  So I can
> change
>> the semantics to find the place the element *would* be.
>> myArray[20..41];
>> and it will find all elements >= 20 and < 41, regardless of whether
> 20 and
>> 41 were valid elements.
>> Hm... can you post this as an enhancement to dcollections so it's
> not
>> forgotten?
>> http://www.dsource.org/projects/dcollections/newticket
>> -Steve
>
> Thanks! I created a new ticket... by the way - is there any bug in
> DMD 2.053 by using my own opCmp? The following code throws me an
> HiddenFuncException:
>
> private import std.stdio : writeln;
>
> class Example {
>
> 	int pId;
>
> 	this(int id) {
>
> 		pId = id;
>
> 	}
>
> 	int opCmp(ref Example other) {

The signature of this function must be

int opCmp(Object other)

Note, also, that ref is unnecessary, as all objects (i.e. class instances)  
are passed by reference.

-Steve