Enumeration Syntax and Semantics

A Slice enumerated type definition looks identical to C++:

enum Fruit { Apple, Pear, Orange };

This definition introduces a type named Fruit that becomes a new type in its own right. Slice guarantees that the values of enumerators increase from left to right, so Apple compares less than Pear in every language mapping. By default, the first enumerator has a value of zero, with sequentially increasing values for subsequent enumerators.

Slice enumerator symbols enter the enclosing namespace scope, so the following is illegal:

enum Fruit { Apple, Pear, Orange };
enum ComputerBrands { Apple, IBM, Sun, HP };    // Apple redefined

The example below shows how to refer to an enumerator from a different scope:

module M {
    enum Color { red, green, blue };
module N {
    struct Pixel {
        M::Color c = M::blue;

Slice does not permit empty enumerations.

Custom Enumerator Values

Slice also permits you to assign custom values to enumerators:

const int PearValue = 7;
enum Fruit { Apple = 0, Pear = PearValue, Orange };

Custom values must be unique and non-negative, and may refer to Slice constants of integer types. If no custom value is specified for an enumerator, its value is one greater than the enumerator that immediately precedes it. In the example above, Orange has the value 8.

The maximum value for an enumerator value is the same as the maximum value for int, 2 31 - 1.

Slice does not require custom enumerator values to be declared in increasing order:

enum Fruit { Apple = 5, Pear = 3, Orange = 1 };   // Legal

Note however that when there is an inconsistency between the declaration order and the numerical order of the enumerators, the behavior of comparison operations may vary between language mappings.

For an application that is still using version 1.0 of the Ice encoding, changing the definition of an enumerated type may break backward compatibility with existing applications. For more information, please refer to the encoding rules for enumerated types.

See Also