How objects are initialized in delphi XE vs XE4

Question

I have a class

type
  TLoadOption = class
  private
    FAutoSearch: Boolean;
  public
    property AutoSearch: Boolean read FAutoSearch write FAutoSearch;
  end;

In one of the functions i am creating the object of the class in stack

procedure MyView.InitializeForm(const aMsg: MyMsg);
//---------------------------------------------------------------------------
var
  Options: TLoadOption;
begin

  if aMsg.OptionalObject <> nil then
   Options := aMsg.OptionalObject as TLoadOption;

  if Assigned(Options) and Options.AutoSearch then
    DoRefresh;
end;

I am not passing anything in aMsg so ideally Options is not set.

In Delphi XE by default Options is set as nil and so this DoRefresh is not called but when i execute the same code in Delpi XE4 the options is initialized with some random value and AutoSearch becomes true always and it results in calling this DoRefresh function which is undesired.

I am wondering if there are any compiler options that set default values to uninitialized variable. My only solution as of now is like this

 procedure MyView.InitializeForm(const aMsg: MyMsg);
    //---------------------------------------------------------------------------
    var
      Options: TLoadOption;
    begin
      Options := nil;

      if aMsg.OptionalObject <> nil then
       Options := aMsg.OptionalObject as TLoadOption;

      if Assigned(Options) and Options.AutoSearch then
        DoRefresh;
    end;

is this a correct way?

Answer 1

As the other answers already said the local variable is not initialized. However what I like to add here is that as is nil safe. That means you don't need to check if aMsg.OptionalObject is assigned. You can just write:

var
  Options: TLoadOption;
begin
  Options := aMsg.OptionalObject as TLoadOption;

  if Assigned(Options) and Options.AutoSearch then
    DoRefresh;
end;

Keep in mind that it will throw an exception if OptionalObject does not inherit from TLoadOption. The code looks as that is always the case. So if you are sure about that you can use a hardcast:

begin
  if Assigned(aMsg.OptionalObject) and TLoadOption(aMsg.OptionalObject).AutoSearch then
    DoRefresh;
end;

Answer 2

A local class is not initialized. You need to set it to nil before testing its assignment.

See Are delphi variables initialized with a value by default?.

Only local reference-counted variables are initialized (example: String,dynamic arrays,interface,variants).

If you are targeting mobile platforms, where ARC (automatic reference counting) is introduced, classes are reference counted though. See Automatic Reference Counting in Delphi Mobile Compilers.

Answer 3

No. Assuming that TLoadOption is an object (unmanaged reference type) you have to initialize local variables yourself. There is no option to have them initialized for you. Local variables for reference types (except for managed types like strings, etc) that are uninitialized will always contain whatever garbage data was in that location on the stack. This makes use of Assigned impossible.

You might just simplify your code a bit, but this is about as short as it can get.

var
  Options: TLoadOption;
begin
  if aMsg.OptionalObject <> nil then begin
    Options := aMsg.OptionalObject as TLoadOption;
    if Options.AutoSearch then DoRefresh;
  end;
end;

Answer 4

Options is a local variable, of a non-managed type. Which means that it is not initialized. It can have any value until you initialize it. If the variable sometimes happens to have the value nil without you having initialized it, then that's just unlucky for you.

You must initialize local variables before attempting to read them.

Answer 5

You don't need local var at all.

procedure MyView.InitializeForm(const aMsg: MyMsg);
begin
  if Assigned(aMsg.OptionalObject)
    and (aMsg.OptionalObject is TLoadOption)
    and (aMsg.OptionalObject as TLoadOption).AutoSearch
  then
    DoRefresh;
end;