The question is not about interfacing with other languages, but exceptionally
about interfacing of Nim modules with each other. The C language allows to hide
internals of a type declaration but still have type checking using just
"half-anonymous" `struct BoxOfStuff *` pointer. I want this functionality in
Nim. And even more: I want to declare "half-anonymous" reference instead of
pointer.
I use "half-anonymous" term to distinguish from "fully-anonymous" pointer which
is simply `void*`.
Here what I figured out so far, using "fully-anonymous" pointers in Nim:
* * *
warehouse.nim:
# Does Nim allow to declare half-anonymous pointer like in 'C' below?
# typedef struct BoxOfStuff * pBox;
# no need to include file where contents of BoxOfStuff is
# defined since here we don't care
#struct Warehouse {
# pBox shelf[]; #c-compiler ensures type of items is pBox. What about
Nim?
#}
type
Warehouse = object
shelf : seq[pointer] # I want anonymous references with type
checking here. How?
rWarehouse = ref Warehouse
box_of_eggs.nim:
import warehouse
# this file is not imported by warehouse.nim
type
BoxOfEggs = object
# some stuff
rBoxOfEggs = ref BoxOfEggs
# example push/pop functions allowing type checking:
#
proc pushbox* (w:rWarehouse, b:rBoxOfEggs) {.inline.} =
GC_ref(b) # NOTE: it will crash without it, because we assign into
anonymous ptr
w.shelf.add(cast[pointer](b))
proc popbox* (w:rWarehouse) : rBoxOfEggs {.inline.} =
result = cast[rBoxOfEggs](w.shelf.pop)
GC_unref(result)
