Ada Programming/Attributes/'Val

Attributes 'Val __TOC__ Description The 'Val attribute is defined for all discrete types. It is a function returning that value of the base type of S having the argument's position number; the prefix S must be a subtype name. (Any specific integer type is implicitly converted to universal_integer.) function S'Val (Arg: universal_integer) return S'Base; If no value of the type of S has the position number Arg, the Constraint_Error exception is raised. Note that representation clauses do not affect position numbering. Whatever underlying value the enumerated value has, the position number will remain the same. Example Declare a discrete type; the compiler will assign the internal representation as 0 .. 2 identical to the position numbers. type My_Enum is (Enum1, Enum2, Enum3); Declare a discrete type and explicitly set the internal representation. Note that the position numbers are still 0 .. 2. type My_Other_Enum is (Value1, Value2, Value3); for My_Other_Enum use (Value1 => 2, Value2 => 4, Value3 => 6); Assert (My_Enum'Val(0) = Enum1); OK Assert (My_Enum'Val(1) = Enum2); OK Assert (My_Enum'Val(2) = Enum3); OK Assert (My_Other_Enum'Val(0) = Value1); OK Assert (My_Other_Enum'Val(1) = Value2); OK Assert (My_Other_Enum'Val(2) = Value3); OK Assert (My_Enum'Val(3) = Enum3); Wrong Assert (My_Other_Enum'Val(2) = Value1); Wrong Assert (My_Other_Enum'Val(4) = Value2); Wrong Assert (My_Other_Enum'Val(6) = Value3); Wrong Other example: type Color is (RED, BLUE, WHITE); OBJECT : Color := WHITE; begin Put (Color'Val (1)); give BLUE The internal representation can only be queried via Unchecked_Conversion. See also The inverse of the 'Val attribute is 'Pos. Wikibook Ada Programming Ada Programming/Attributes Ada Programming/Attributes/'Pos Ada Reference Manual 13 3 Operational and Representation Attributes K Language-Defined Attributes Val