RFC: untyped(expr) for untyped params in overloaded routines

[timotheecour]

proposal:

add untyped typeclass, useful for overload resolution.

Example

proc fn(a: untyped): untyped = 1
proc fn(a: typed): untyped = 2
proc fn(a: int): untyped = 3

assert fn(nonexistant.untyped) == 1
assert fn(nonexistant) # CT error
assert fn("abc") == 2
assert fn(2) == 3
assert fn(2.untyped) == 1

assert untyped(nonexistant) is untyped
assert untyped(2) is untyped

links

• this is compatible with iterable[T] refs iterable[T] by timotheecour · Pull Request #17196 · nim-lang/Nim and doesn't reduce the need for iterable[T]

• Improve overloaded resolution for template with untyped parameter nim-lang/RFCs#402