[fpc-pascal] Functions with out parameters

[Damien Gerard]

I have the following function :

procedure Foo(const AText: UTF8String; out AValue: UTF8String);
begin
   ShowMessage(AText); //
   AValue := 'A custom value';
end;

procedure AnotherMethod;
var s: UTF8String;
begin
   s := 'Some text';
   Foo(s, s);
   // Do something with `s`
end;


If you have this, the showmessage display an empty string and  
sometimes the app crashes. I had a doubt so I tried this :

procedure AnotherMethod;
var s, t: UTF8String;
begin
   s := 'Some text';
   t := s;
   Foo(t, s);
   // Do something with `s`
end;

And it works well the app never crash and all my variables are  
correct. So I guess the two parameters share the same pointer. It  
seems logic to me in this case.

However, is there a way the compiler produces an error in this case ?  
I suppose there is a similar case with the 'var' keyword.


--
Damien Gerard
milipili at shikami.org

"Intelligence is 10 million rules."
    -- Douglas Lenat