Generics constructor with parameter constraint?

Question

TMyBaseClass=class
  constructor(test:integer);
end;

TMyClass=class(TMyBaseClass);

TClass1=class()
  public
    FItem: T;
    pr         


        

Answer 1

type
  TBase = class
    constructor Create (aParam: Integer); virtual;
  end;

  TBaseClass = class of TBase;

  TFabric = class
    class function CreateAsBase (ConcreteClass: TBaseClass; aParam: Integer): TBase;
    class function CreateMyClass(aParam: Integer): T;
  end;

  TSpecial = class(TBase)
  end;

  TSuperSpecial = class(TSpecial)
    constructor Create(aParam: Integer); override;
  end;

class function TFabric.CreateAsBase(ConcreteClass: TBaseClass; aParam: Integer): TBase;
begin
  Result := ConcreteClass.Create (aParam);
end;

class function TFabric.CreateMyClass(aParam: Integer): T;
begin
  Result := CreateAsBase (T, aParam) as T;
end;

// using
var
  B: TBase;
  S: TSpecial;
  SS: TSuperSpecial;
begin
  B := TFabric.CreateMyClass  (1);
  S := TFabric.CreateMyClass  (1);
  SS := TFabric.CreateMyClass  (1);