Question

I am using Delphi. I have a root class and many derived class from the root, the name of the class says TROOT, TA, TB, TC … In the code, I have some code to control the flow of the program by following code

var
  obj :TROOT;
begin
  if ((obj is TA) or (obj is TB) or (obj is TC) or (obj is TD)) then
  begin
    // some other codes here
  end
end;

this code works good but then I extend my code so more subclasses are derived from TROOT and that swtich appears at more than one place in the program. Is there any way I can put the class type into a set or array and have some psudeo code like following so I don’t have to modify everywhere when the code is extended?

classarray = {TA, TB, TC, TD, TE, TF};
if (obj in classarray) then
begin
  // put my code here
end

Thanks.

Answer 1

You can of course put the classes in an array. Declare the types like this:

type
  TRootClass = class of TRoot;
  TRootClassArray = array of TRootClass;

Declare and populate the array:

var
  RootClasses: TRootClassArray;

SetLength(Classes, 4);
RootClasses[0] := TA;
RootClasses[1] := TB;
RootClasses[2] := TC;
RootClasses[3] := TD;

Then you can test the contents of the array:

var
  c: TRootClass;

for c in RootClasses do
  if obj is c then
    // ...