So why doesn't popFront return an element?

[Andrej Mitrovic]

This leads me to another question I've always wanted to ask. A call such as:

auto b=map!foo(map!bar1(map!bar2(a));

This constructs a lazy range. What I'm wondering is if there are any
performance issues when constructing long chains of ranges like that,
since this basically routes one function to the next, which routes to
the next, etc. E.g:

auto a = [1, 2];
auto b = retro(a);
auto c = retro(b);
auto d = retro(c);

Under the surface, I assume calling d.front would mean the following calls:
d.front()->c.back()->b.front()->a.back()

Or another example:
auto b = retro(retro(a));

Can the compiler optimize the second case and convert b.front to just
do one field access?