Transient ranges

[Dicebot via Digitalmars-d]

On Sunday, 29 May 2016 at 17:25:47 UTC, Steven Schveighoffer 
wrote:
> What problems are solvable only by not caching the front 
> element? I can't think of any.

As far as I know, currently it is done mostly for performance 
reasons - if result is fitting in the register there is no need 
to allocate stack space for the cache, or something like that. 
One of most annoying examples is map which calls lambda on each 
`front` call : 
https://github.com/dlang/phobos/blob/master/std/algorithm/iteration.d#L587-L590

> And there is no way to define "transient" ranges in a way other 
> than explicitly declaring they are transient. There isn't 
> anything inherent or introspectable about such ranges.

I don't really care about concept of transient ranges, it is the 
fact there is no guarantee of front stability for plain input 
ranges which worries me.