opIndex, opSlice, length for joiner?

[Maverick Chardet via Digitalmars-d]

On Friday, 22 January 2016 at 01:02:10 UTC, Andrei Alexandrescu 
wrote:
> On 01/21/2016 05:22 PM, Maverick Chardet wrote:
>> Just a question: is it possible for a range to be considered 
>> infinite
>> and at the same time have a length? I suppose that if it is 
>> possible,
>> such a range would be ill-formed...
>
> Indeed that range would be ill-formed. -- Andrei

Okay so I'll just use an assert!


Something is bothering me though, I'm wondering why walkLength 
does not save the range when possible (when it is an input 
range)? For now it's just making a copy, couldn't it be 
problematic in some cases? The current code is:


auto walkLength(Range)(Range range)
     if (isInputRange!Range && !isInfinite!Range)
{
     static if (hasLength!Range)
         return range.length;
     else
     {
         size_t result;
         for ( ; !range.empty ; range.popFront() )
             ++result;
         return result;
     }
}


Why not something like this:


auto walkLength(Range)(const ref Range range)
     if (isInputRange!Range && !isInfinite!Range)
{
     static if (hasLength!Range)
         return range.length;
     else
     {
         size_t result;
         static if (isForwardRange!range)
         {
             Range rangeCopy = range.save;
         }
         else
         {
             Range rangeCopy = range;
         }
         for ( ; !rangeCopy.empty ; rangeCopy.popFront() )
             ++result;
         return result;
     }
}


Maverick Chardet