[fpc-devel] FPC Delphi compatibility question...

Bruce Tulloch bruce at causal.com
Fri Jun 19 06:45:10 CEST 2009

I found what appears to a subtle difference between the Delphi & Kylix3
handling of dynamic array assignment and FPC in Delphi mode. If an
assignment is made along the lines:

    TArray : array of Integer;

    A, B : TArray;
    I : Integer;

    function F ( C : TArray ) : TArray;
       { does nothing }

    for I := 0 to 3 do
       B[I] := I;

    A := Copy(B);
    A := F(B); { what is the correct answer here? }

a question arises as to the value of A. Should it be nil or should it be
a copy of B?

Delphi and Kylix assume that because the function F does not assign a
value to Result (ie, does not assign a return value) that the Lvalue
assigned from F remains unchanged.

FPC assigns nil to A which IMHO is correct, but not when run in "bug for
bug" Delphi compatibility mode.

Obviously F not assigning Result is a programming error, but
unfortunately it can be a common one in legacy code.

What do others think about this compatibility difference?

Should it be fixed or should (possibly large) legacy codebases be debugged?

Cheers, Bruce.

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