We call this nim-c-nim sandwich. How it works is that we compile nim-c and
create the DLL with a basic C interface. Then we create another nim file (it
kind of looks it was generated by c2nim) that does the export.
original nim function:
proc simpleCall(a: int): int =
## Returns the integer passed in.
return a
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c function signature:
long long test_simple_call(long long a);
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nim's function DLL importer:
proc test_simple_call(a: int): int {.importc: "test_simple_call", cdecl.}
proc simpleCall*(a: int): int {.inline.} =
result = test_simple_call(a)
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We do a function wrapper around the C function because some times one needs to
convert from cstring to string, or other types, or insert exception handling.
Some times its wrappers on both ends, to pass a string we convert it to cstring
and then back to string. This allows programs using the DLL to use --gc:refc
while DLL basically require use of --gc:arc or --gc:orc.
