Oh, right! I guess it's testing it on untyped rather than the actual type in
the macro. Anyways, this one is definitely working, it just tests for
void-typed arguments:
import macros
import typetraits
import strformat
macro fun*(n: varargs[typed]): typed =
result = newNimNode(nnkStmtList, n)
var echoedCount = 0
for x in n:
if x.getTypeInst.typeKind != ntyVoid:
result.add(newCall("echo", x))
echoedCount += 1
result.add(newCall("echo", newStrLitNode($(echoedCount))))
proc bar() = echo "ok"
fun(1+1) # n.len=1
fun() # n.len=0
# comment this to make it work
fun(bar())
> isn't that a better behavior? if not what would be downsides of that?
No, I think automatically filtering void arguments in a macro is not a better
or intuitive behavior. What if you remove a return type from a function and the
compiler just silently starts ignoring it in argument lists instead of
producing a type mismatch error? That seems like it could be an interesting
source of bugs.
I guess what you're asking for is not SFINAE, but it feels similar -- it's a
hack used to make template systems have some limited metaprogramming. I think
that you'll find that sort of thing is not necessary with Nim, you can just
write a macro that does what you want. Is there something specific that you're
trying to do that requires the argument-ignoring approach used in D? Maybe we
could help you come up with a good solution for it in Nim.
