14 Enumeration conversions

14.1 Conversions between enumerations and integers [conv.enum.scpp]

1. Except as modified by this subclause, [dcl.enum], [expr.static.cast], and [expr.cast] apply unchanged to enumeration types in an SCPP26 program.

2. An expression of enumeration type can be explicitly converted to an integral type if, and only if, the corresponding conversion is well-formed in C++26. Such a conversion is permitted whether it is spelled as a static_cast ([expr.static.cast]) or as an explicit-type-conversion ([expr.cast]).

[Note: static_cast<int>(color) and int(color) are examples of the conversions permitted by (2). — end note]

3. An explicit conversion whose source expression is of integral type and whose destination type is an enumeration type is ill-formed.

[Note: static_cast<Color>(n) and Color(n) are both rejected. — end note]

4. A program that needs to convert an integer value to an enumeration type shall call scpp::enum_cast<T>(value), where T denotes that enumeration type. scpp::enum_cast<T>(value) shall return std::expected<T, scpp::enum_cast_error>.

5. scpp::enum_cast<T>(value) succeeds if and only if value is equal to the underlying integer value of one of T’s enumerators. Otherwise it shall return an error value of type scpp::enum_cast_error, whose invalid_value enumerator denotes that failure. No other unchecked or ordinary cast-based conversion from an integer value to an enumeration type is provided.

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