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 __bool__()) rather than absence.

Lexer note: As of the ? early-return operator, ?? is no longer a single token — it is two ? tokens at the lexer level. The semantics of ?? are unchanged; the parser distinguishes ?? (null-coalesce) from the postfix ? (early-return) using a token-counting rule. See the Question-Mark Operator for the disambiguation details.

Note: Unlike Python, Sharpy's or operator always returns bool, not the operand value. "" or "Anonymous" returns True (bool), not "Anonymous" (str). This is because Sharpy's or maps to C#'s || operator, which produces a boolean result.

name = "" ?? "Anonymous"    # name = "" (not None, so left side kept)
name = None ?? "Anonymous"  # name = "Anonymous" (None, so right side used)

# or returns bool, not the operand value (unlike Python)
result = "" or "Anonymous"    # result = True (bool, not "Anonymous")
result = None or "Anonymous"  # result = True (bool, not "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