Null-Coalescing Operator

The ?? operator provides a default value when the left operand is absent. It works with both T? (Optional[T]) and T | None (C# nullable):

# With T? (Optional)
name: str? = get_name()
display = name ?? "Anonymous"

# With T | None (C# nullable)
raw: str | None = dotnet_api()
display = raw ?? "Anonymous"

# Chaining
result = first ?? second ?? default_value

This contrasts with the or operator which tests for truthiness (via __true__() and __false__() dunders if defined, or __bool__() otherwise), rather than absence:

name = "" ?? "Anonymous"    # name = ""
name = "" or "Anonymous"    # name = "Anonymous"

name = None ?? "Anonymous"  # name = "Anonymous"
name = None or "Anonymous"  # name = "Anonymous"

Implementation - ✅ Native - For T | None, maps to C# ?? operator. - 🔄 Lowered - For T? (Optional[T]), compiler generates match on Some/None().

Optional (Tagged Union)

The Optional[T] tagged union (written as T?) works with null coalescing, with its empty case (None()) being treated similarly to bare None:

maybe_int: int? = Some(5)
val = maybe_int ?? 0  # val = 5

maybe_int = None()
val = maybe_int ?? 0  # val = 0