Is Delphi "with" keyword a bad practice?

Question

I been reading bad things about the with keyword in delphi but, in my opinion, if you don't over use it. It can make your code look simple.

I often put all my TClientDataSets and TFields in TDataModules. So in my forms I had code like this

procedure TMyForm.AddButtonClick(Sender: TObject); begin     with LongNameDataModule do   begin      LongNameTable1.Insert;      LongNameTable1_Field1.Value := "some value";      LongNameTable1_Field2.Value := LongNameTable2_LongNameField1.Value;      LongNameTable1_Field3.Value := LongNameTable3_LongNameField1.Value;      LongNameTable1_Field4.Value := LongNameTable4_LongNameField1.Value;      LongNameTable1.Post;   end end; 

without the with keyword I have to write the code like this

    procedure TMyForm.AddButtonClick(Sender: TObject);     begin                   LongNameDataModule.LongNameTable1.Insert;       LongNameDataModule.LongNameTable1_LongNameField1.Value := "some value";        LongNameDataModule.LongNameTable1_LongNameField2.Value :=                LongNameDataModule.LongNameTable2_LongNameField1.Value;        LongNameDataModule.LongNameTable1_LongNameField3.Value :=                LongNameDataModule.LongNameTable3_LongNameField1.Value;        LongNameDataModule.LongNameTable1_LongNameField4.Value :=                LongNameDataModule.LongNameTable4_LongNameField1.Value;        LongNameDataModule.LongNameTable1.Post;     end; 

I think is easier to read using the with keyword.

Should I avoid using the with keyword?

Answer 1

The biggest danger of with, outside of pathological conditions like "with A, B, C, D" is that your code can silently change meaning with no notice to you. Consider this example:

with TFoo.Create try   Bar := Baz;   DoSomething(); finally   Free; end; 

You write this code knowing that Bar is a property of TFoo, and Baz is a property of the type containing the method which has this code.

Now, two years later, some well-meaning developer comes in adds a Baz property to TFoo. Your code has silently changed meaning. The compiler won't complain, but the code is now broken.