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I came across some strange behaviour in Delphi XE4.
I can't declare a set type within a generic class, where the ordinal type is declared within the same class.
For example:
TTest<T> = class(TObject)
type
TEnumType = (eOne, eTwo, eThree);
TEnumTypes = set of TEnumType;
end;
The above does not compile. The compiler emits error "E2001: Ordinal type required".
A non-generic class like
TTest = class(TObject)
type
TEnumType = (eOne, eTwo, eThree);
TEnumTypes = set of TEnumType;
end;
does compile.
For the generic class to compile successfully, the ordinal type has to be declared outside the class:
TEnumType = (eOne, eTwo, eThree);
TTest<T> = class(TObject)
type
TEnumTypes = set of TEnumType;
end;
486
Yes, we can define an enumeration inside a class. You can retrieve the values in an enumeration using the values() method.
On a technical level, there's nothing wrong with using an enum as the type used in a generic type.
An enum is defined using the enum keyword, directly inside a namespace, class, or structure. All the constant names can be declared inside the curly brackets and separated by a comma. The following defines an enum for the weekdays. Above, the WeekDays enum declares members in each line separated by a comma.
The enum is a default subclass of the generic Enum<T> class, where T represents generic enum type. This is the common base class of all Java language enumeration types. The transformation from enum to a class is done by the Java compiler during compilation. This extension need not be stated explicitly in code.
This is indeed a bug that is fixed in later versions. Your code compiles in XE7 for instance. Quite possibly it will compile in XE5 or XE6, but I don't have them immediately to hand to check.
136
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