"IndexType" for ranges

[monarch_dodra]

On Tuesday, 2 October 2012 at 16:09:16 UTC, Peter Alexander wrote:
> On Tuesday, 2 October 2012 at 13:17:45 UTC, monarch_dodra wrote:
>> If you've ever worked on a template that needs to index a 
>> range, you may have run into this problem: What is the type 
>> you should use to index an RA range?
>
> Forgive my ignorance. What's wrong with size_t?

This is what happens when you use size_t:

//----
import std.range;
import std.algorithm;

struct ZeroToTen
{
     ushort first = 0;
     ushort last = 10;
     @property bool empty(){return first == last;}
     @property ushort front(){return first;}
     void popFront(){++first;}
     @property ushort back(){return last;}
     void popBack(){--last;}
     @property ZeroToTen save(){return this;}
     @property ushort length(){return cast(ushort)(last - first);}
     ushort opIndex(ushort n){return cast(ushort)(first + n);}
}

void main()
{
     ZeroToTen ztt;

     static assert(hasLength!ZeroToTen);      //OK: normal
     static assert(isRandomAccess!ZeroToTen); //Ok... But I don't 
like where this is going...

     auto r = assumeSorted(ztt); //DERP!
}
//----
\src\phobos\std\range.d(6909): Error: function 
main.ZeroToTen.opIndex (ushort n) is not callable using argument 
types (uint)
\src\phobos\std\range.d(6909): Error: cannot implicitly convert 
expression (i) of type uint to ushort
\src\phobos\std\range.d(7346): Error: template instance 
std.range.SortedRange!(ZeroToTen,"a < b") error instantiating
//----