[Lazarus] try finally exit

[Hans-Peter Diettrich]

Ludo Brands schrieb:

> As an example consider the following routine:
> 
> Procedure Doit (Name : string);
> Var F : Text;
> begin
>   Try
>     Assign (F,Name);
>     Rewrite (name);
>     ... File handling ...
>   Finally
>     Close(F);
>   end;

That's a questionable example. Which of the actions are required for 
proper operation of Close?

It's much clearer with objects:

   MyObj := TMyClass.Create;
   //only now the local variable has an valid value
   try
     //do something with MyObj
   finally
     MyObj.Free;
   end;

Wrong placement of the "try" can result in references to uninitialized 
local variables in the "finally" code, with unpredicatable effects.

That's why I prefer to initialize local object variables to Nil, before 
entering an try-finally block where they are created. This pattern 
allows to use an single try-finally block to protect multiple local objects:

   obj1 := nil;
   obj2 := nil;
   ...
   try
     obj1 := T1.Create;
     ...
   finally
     obj1.Free;
     obj2.Free;
     ...
   end;

DoDi