[fpc-devel] 019605: Safety check for "const s: string" (similar to Range or Overflow checks)

[Florian Klämpfl]

Am 23.06.2011 22:31, schrieb Martin:
> 
> This is about finding screwups of the refcount. The data modification
> detection of strings is a side effect only.
> 

Why is a "screwup" of the ref. count a problem? It is only a problem if
it gets 0 and the string is disposed?

> 
> 
> 
> Anyway, I repeat. I do not try to detect, if the string content was
> changed => that is a side effect
> 
> I try to catch issues with the refcount.
> 
> They do not happen, if the string is part of a const param record
> 

Why not?

This ...

{$h+}
type
  tr = record
    s : string;
  end;
var
  r : tr;

procedure proc;
  begin
    r.s:='1234';
  end;

procedure Foo(const r : tr);
  begin
    proc;
    // r.s is invalid now ...
  end;

begin
  setlength(r.s,10);
  Foo(r);
end.

... hurts as well because r is passed by value because it is small.