On Monday, 12 November 2012 at 20:52:07 UTC, Jonathan M Davis
wrote:
That wouldn't work. It's the complete opposite of what a
generative range would require if it generates the return value
in front. Narrow strings in particularly would be screwed by
it, because their front is calculated, and
since it's a free function, as is popFront, there's no way
to save the return value of front in popFront. It has to
be calculated in front, and it's not at all transient.
It also screws with the ability to have sealed containers,
since in that case, something like front would never
return by ref.
The refness of front's type really shouldn't have anything
to do with its transience. They're completely unrelated.
I didn't understand any of those arguments, so perhaps I still
don't fully comprehend this issue.
Persistence
-----------
I thought persistent X means that there's a dedicated storage
space for X where it will exist after front returns and X's value
will not be tampered with by calling popFront. That notion of
persistence led to me into thinking that persistent front could
(and really should) return either a reference to X or a const
reference if the range doesn't want to allow mutation through
front.
Transience
----------
The other side of the coin in my thinking was that transient
means that X doesn't have a dedicated storage space. So transient
X could be a variable that's local to function front, or it could
be that X is stored in a buffer and will exist there after front
returns, but the buffer would be overwritten by a call to
popFront. And that notion of transience led me into thinking that
transient front could never return a reference.
NOTE: All of the above assumes that D were designed so that all
types had value semantics.
