Question

Consider the following example (I am using Delphi XE):

program Test;

{$APPTYPE CONSOLE}

type
  TTestClass<T> = class
  private
    class constructor CreateClass();
  public
    constructor Create();
  end;

class constructor TTestClass<T>.CreateClass();
begin
  // class constructor is not called. this line never gets executed!
  Writeln('class created');
end;

constructor TTestClass<T>.Create();
begin
  // this line, of course, is printed
  Writeln('instance created');
end;

var
  test: TTestClass<Integer>;

begin
  test := TTestClass<Integer>.Create();
  test.Free();
end.

The class constructur is never called and hence the line ‘class created’ is not printed.
However, if I remove the generalisation and make TTestClass<T> into a standard class TTestClass, everything works as expected.

Am I missing something out with generics? Or it simply doesn’t work?

Any thoughts on this would be apprechiated!

Thanks,
–Stefan–

Answer 1

Looks like a compiler bug. The same code works if you move the TTestClass declaration and implementation to a separate unit.

unit TestClass;

interface
type
  TTestClass<T> = class
  private
    class constructor CreateClass();
  public
    constructor Create();
  end;

var
  test: TTestClass<Integer>;

implementation

class constructor TTestClass<T>.CreateClass();
begin
  Writeln('class created');
end;

constructor TTestClass<T>.Create();
begin
  Writeln('instance created');
end;

end.