Delphi: array of Char and TCharArray "Incompatible Types"

Question

I've run across this "Incompatible types" error in the comment below a few times, and never been happy with why this isn't directly supported in Delphi 2007:

program Project1; {$APPTYPE CONSOLE}

type TCharArray = array of Char;

procedure DoArray(Chars: array of Char);
begin
end;

function ReturnTCharArray: TCharArray;
var CharArray: TCharArray;
begin
  Result := CharArray;
end;

begin
  DoArray(ReturnTCharArray); // [DCC Error] Project1.dpr(18): E2010 Incompatible types: 'Array' and 'TCharArray'
end.

Shouldn't it be possible to make an array type "aliased" to another array type compatible with each other? Assuming I can't change the declaration of DoArray (it is part of a third party library), how do I write a function returning an array of char compatible with DoArray's param? The straightforward "function ReturnAChar: array of Char;" results in an "Identifier expected but 'ARRAY' found" error. I even tried changing the function returning the array to a procedure with a var "array of Char" pram, but that also doesn't allow setting the length of the "array of Char" param in the procedure ("Constant object cannot be passed as var parameter").

Answer 1

This may actually be a compiler bug (or a limitation that was never documented properly). I did some experimentation and found that you can pass a dynamic array (typed or not) to a procedure expecting an open array for almost every type... except Char and WideChar.

See Is a dynamic array of Char allowed when the parameter type is open array of Char? for a description of the problem and a possible work around.