Why is the Compiler warning that variable may not be initialized?

Question

I am getting a compiler warning I don't understand:

procedure Test;
var
  Var1: Integer;
begin
    while True do
    begin
        try
            if System.Random > 0.5 then
            begin
                ShowMessage('Skipping');
                continue; // If I remove this line, the warning goes away
            end;
            Var1:=6;
        except on
            E:Exception do
            begin
                ShowMessage('Error');
                raise;
            end;
        end;
        ShowMessage(IntToStr(Var1)); // Compiler warning on this line
    end;
end;

When I compile this in Delphi 2010 I get:

[DCC Warning] OnlineClaimManagerMainU.pas(554): W1036 Variable 'Var1' might not have been initialized

If I remove the call to 'continue', the warning goes away.

Also, if I remove the try/except clause (and leave the continue), the warning goes away.

How will execution get to the line in question without Var1 being initialised?

The compiler's analysis is not as deep as yours. It can't be sure that Var1 has been initialised. You know that Var1 is always initialised but the compiler does not have your analytic talents. — David Heffernan
So... why does removing the continue fix it? The same problem would apply. Or is it just the sheer complexity of the combination of both that blows the compilers mind? — awmross
I guess the presence of the continue means the compiler's analysis is harder. Interestingly I once had some code that I knew was fine but that the compiler warned about, in x86 but not x64. I made the obvious change and then x86 compiler was quiet, but x64 complier whined!! Very odd. — David Heffernan
@cesar that's missing the point. The question is about why the compiler warns about something that can never happen. — David Heffernan

Unknown Unknown · Accepted Answer · 2012-07-19T06:13:56

Var1 will always be initialised before it is used. The compiler gets confused by try-except handling: your code is too complex for the compiler to be able to actually determine that Var1 is always initialised. It sees there may be a handled exception before Var1:=6;, which would leave Var1 uninitialised, but it doesn't see that that exception will always be re-raised.

Why is the Compiler warning that variable may not be initialized?

3 Answers