A cool feature introduced in Delphi 10.2 Tokyo: often [RSP-17326] with statements generate W1048 unsafe typecast warning – Embarcadero Technologies.

Only 2 upvotes, so I assume the “anti with camp” people are finally winning (:

Notes:

• that not all with statements generate a W1048 warning. It looks like the ones using local variables don’t, but parameters, properties and fields to.
• when generated, they are always of this form: W1048 Unsafe typecast of '%s' to 'Pointer'
• I only found one other public report searching for “w1048” “to ‘Pointer'” – Google Search:
  • [WayBack] unsafe typecast / Delphi / Sql.ru ([Archive.is] Google Translate)

Quoted from the bug-report (as they cannot be archived in the wayback machine)

1. RAD Studio
2. RSP-17326

with statements generate W1048 unsafe typecast warning

Details

• Type: Bug
• Status: Reported
• Priority: Major
• Resolution:Unresolved
• Affects Version/s:10.2 Tokyo
• Fix Version/s:None
• Component/s:Delphi Compiler
• Labels: None

• Build No: 25.0.25948.9960
• Platform: All
• Language Version: English
• Edition: Enterprise
• InternalID: RS-82298
• InternalStatus: Validation

Description

All with statements generate this warning. I am on board with the theory that all with statements are inherently somewhat unsafe, but with 1.5 million lines of legacy code (and over 500 new warnings), I would significantly prefer to have a separate warning for with statements.
As it happens I would like to go through and do this work, especially if we can have refactoring to restore non-with code – see RSP-13978. BUT, Godzilla is generating new extra warnings (including unsafe typecasts) in this legacy code and I would prefer to be able to attack these first and attend to with statements later.

Activity

Comments

Jira-Quality Sync Service added a comment – 12/Apr/17 10:24 AM

Jason Sprenger requested more info in order to validate the issue and commented: Not any code involving “with” statements produces an unsafe typecast warning.

For instance,

program RS82298;

{$APPTYPE CONSOLE}

uses
  System.SysUtils;

procedure Use(var X);
begin<
end;

type
  TMyClass = class
    FValue: Integer;
    property Value: Integer read FValue write FValue;
  end;

procedure RunRS82298;
var
  MyClass: TMyClass;
begin
  MyClass := TMyClass.Create;
  with MyClass do
    begin
      Value := 42;
    end;
  with MyClass do
    WriteLn('MyClass.Value=', MyClass.Value);

  Use(MyClass);
end;

begin
  try
    RunRS82298
  except
    on E: Exception do
      begin
        WriteLn('FAIL - Unexpected Exception');
        WriteLn('  ClassName=', E.ClassName);
        WriteLn('    Message=', E.Message);
      end;
  end;
end.

What sort of source involving “with” statements is generating these warnings for you?

With this information our development team can consider addressing your particular circumstance.

Stuart Seath [X] (Inactive) added a comment – 12/Apr/17 12:50 PM

Try this (obviously a simple made-up example), and you do need to enable W1048 first in the project options:

program Project18;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

type
  TAnother = class
  private
    FAmbiguous : Boolean;
  public
    property Ambiguous : Boolean read FAmbiguous write FAmbiguous;
  end;

  TFirst = class
  private
    FAnother : TAnother;
  public
    procedure Doit;
  end;

var
  First : TFirst;

{ TFirst }

procedure TFirst.Doit;
begin
  FAnother := TAnother.Create;
  with FAnother do // WARNING
  begin
    Ambiguous := true;
  end;
end;

var
  XAnother : TAnother;

begin
  try
    XAnother := TAnother.Create;
    with XAnother do // NO WARNING HERE
    begin
      Ambiguous := true;
    end;

  except
    on E: Exception do
  Writeln(E.ClassName, ': ', E.Message);
end;
end.

–jeroen