A class definition can contain a type section, const section and a variable section. The type and
constant sections act as a regular type section as found in a unit or method/function/procedure
implementation. The variables act as regular fields of the class, unless they are in a class var
section, in which case they act as if they were defined at the unit level, within the namespace of the
class (section 6.3, page 308).
However, the visibility of these sections does play a role: private and protected (strict or not)
constants, types and variables can only be used as far as their visibility allows.
Public types can be used outside the class, by their full name:
type
TA = Class(TObject)
Public
Type TEnum = (a,b,c);
Class Function DoSomething : TEnum;
end;
Class Function TA.DoSomething : TEnum;
begin
Result:=a;
end;
var
E : TA.TEnum;
begin
E:=TA.DoSomething;
end.
Whereas
type
TA = Class(TObject)
Strict Private
Type TEnum = (a,b,c);
Public
Class Function DoSomething : TEnum;
end;
Class Function TA.DoSomething : TEnum;
begin
Result:=a;
end;
var
E : TA.TEnum;
begin
E:=TA.DoSomething;
end.
Will not compile and will return an error:
tt.pp(20,10) Error: identifier idents no member "TEnum"
Note that for writeable constants, the same rules apply as for class variables with regard to scope
and overriding in descendents:
{$mode delphi}{$J+}
type
TA = class // base type
const CODE: integer = 99;
end;
TB = class(TA);
TC = class(TA);
begin
TA.Code:=0;
TB.Code:=1;
TC.Code:=2;
Writeln(Ta.Code:2,Tb.Code:2,Tc.code:2);
end.
Will write
2 2 2
But
{$mode delphi}{$J+}
type
TA = class // base type
const CODE: integer = -99;
end;
TB = class(TA)
const code : integer = -98;
end;
TC = class(TA)
Const code : integer = -97;
end;
begin
TA.Code:=0;
TB.Code:=1;
TC.Code:=2;
Writeln(Ta.Code:2,Tb.Code:2,Tc.code:2);
end.
Will write
0 1 2