Multiple return value as requirements for safety and performance

[Ilya Yaroshenko via Digitalmars-d]

On Tuesday, 20 December 2016 at 16:34:04 UTC, Walter Bright wrote:
> On 12/20/2016 6:08 AM, Ilya Yaroshenko wrote:
>> No, tuples stores either value or pointer. If it stores 
>> pointer then it is not
>> safe and it is not CTFE.
>
> You can make it safe by using an array rather than a pointer.

Ranges a and b may not be arrays. They just have Range API and 
return front by reference.How this can be handled for CTFE, safe 
code? Would the solution be fast?