how convert the range to slice ?

["Nordlöw" via Digitalmars-d-learn]

On Wednesday, 28 January 2015 at 23:21:34 UTC, Nordlöw wrote:
> I'll dig into it later on...

Is started digging a bit...

The magic happens at line 103 in cast.c.

How do I most conveniently figure out which members (functions) a 
type (e->type) has?

I figured I could check for typical InputRange members and issue 
a hint about using .array if e->type has them.