Difference between input range and forward range

[Jesse Phillips via Digitalmars-d]

On Tuesday, 10 November 2015 at 16:07:01 UTC, Jonathan M Davis 
wrote:
> generic code, you have to consider it to be consumed, because 
> the state of range you passed to foreach is now undefined, 
> since what happens when copying the range is undefined. This is 
> true even if you put a break out of the loop, because the range 
> was copied, and you simply cannot rely on the state of the 
> range you passed to foreach after that copy.

The problem I find with generic code is when the desire is to 
consume the data. Take this example of parsing a data stream.

     auto osmData = datastream.take(size).array;
     datastream.popFrontN(size);
     auto header = BlobHeader(osmData);

http://he-the-great.livejournal.com/49636.html

How do I know if popFrontN is needed? If I was given a value base 
range then it is. If I was given a reference range (in its many 
forms) the extra call to popFrontN will result in an unneeded 
data jump. I could require that a forward range is passed in, 
then I can save() before calling .array and thus always require 
popFrontN.

The best option is probably to use the RefRange wrapper, but it 
does create an annoying element of surprise.