Size of generic type

Question

Is there any way to determine the size in bytes of something like

TItem <T> = record
  Data : T;
end;

Can I write something like

function TItem <T>.GetByteSize : Integer;
begin
if (T = String) then
  Result := GetStringByteSize (Data as String)
else
  Result := SizeOf (Data);
end;

or perhaps with the help of specialization?

function TItem <String>.GetByteSize : Integer;
begin
  Result := GetStringByteSize (Data)
end;

function TItem <T>.GetByteSize : Integer;
begin
  Result := SizeOf (Data);
end;

Thanks!

Answer 1

Is there something wrong with taking the size of the instantiated type?

SizeOf(TItem<string>)

Or you could define GetByteSize like this:

function TItem <T>.GetByteSize : Integer;
begin
  Result := SizeOf(TItem<T>);
end;

Answer 2

No, you can't specialize depending on type as far as I know