Can TBytes, TByteDynArray, Array of Bytes be safely typecasted to each other?

Question

Since TBytes, TByteDynArray, and array of Bytes are all dynamic arrays of bytes, can typed variables be safely typecasted to each other? (If I have a variable of TBytes can I simply typecast to TByteDynArray when using a method that defines parameters as TByteDynArray and vice-versa?)

Answer 1

Such typecasts are perfectly safe in all the Delphi implementations that I have ever encountered.

However, reinterpretation typecasts like this remove type checking, there is always a risk that future changes to the source code can result in hard to trace errors. I would always try to avoid casting if possible. For example, the very simplest thing you can do is to avoid using array of Byte as a type in your code and switch to TBytes.

If you must cast then wrap it up in a function to mitigate the risks I describe above.

function Bytes(const B: TByteDynArray): TBytes;
begin
  Result := TBytes(B);
end;