Enumerations

This page defines enumeration behavior. Common examples are also shown in the Types guide.

Declaration

An enum declares a closed set of named values backed by an integer storage type.

enum NColor = (red, green, blue)
enum NState : uint8 = (idle = 0, running = 10, stopped = 20)

When no storage type is written, the storage type is uint8. An explicit storage type must be one of the fixed-width signed or unsigned integer types from int8 through uint64, and every enumerator value must fit that type.

Implicit values begin at zero and increment from the previous value. An explicit value changes the value from which following implicit enumerators are calculated. After the first enumerator, an explicit value cannot move backward. Every enumerator value must be unique. A duplicate is a compile error, and a numeric value not assigned to an enumerator is not a valid member of the enum.

Naming and Lookup

Qualification uses the enum type name.

var color : NColor = NColor.green

An enumerator may be unqualified when contextual typing identifies exactly one enum type, including initialization, assignment, argument, return, comparison, and case-like contexts supported by the compiler. Otherwise it must be qualified.

Type Safety

An enum is distinct from its storage type and every other enum. There is no implicit conversion to or from integers, and arithmetic is not defined on enum values.

Equality and inequality compare values of the same enum type. Use .ord or Ord(value) explicitly when numeric ordering is intended.

Ordinal Conversion

The read-only .ord property and Ord(value) return the stored integer value. Checked construction uses the enum type's helpers:

var state : NState = NState.FromOrd(10)
var fallback : NState = NState.FromOrd(11, idle)

var output : NState = idle
if NState.TryFromOrd(20, output):
    // output is stopped
endif

FromOrd(value) raises a runtime error if no enumerator has that value. The two-argument overload returns its fallback instead. TryFromOrd returns true and updates the output only for a valid value.

Forward Compatibility

When persistent or wire formats may gain new values, decode with TryFromOrd or the fallback overload rather than assuming every stored integer is currently known.