Delphi XE4 Indy compatibility issue between TBytes and TidBytes
Today I try to compile my XE3 project in XE4. First problem that I face is with Indy's FTCPClient.Socket.ReadBytes() method.
Before it was accepting TBytes type, now it insists on TidBytes.
Definitions: TIdBytes = array of Byte; TBytes, Im not sure I guess it is generics something like TArray which is array of Byte.
Question number 1: Why does compiler complain by saying that'[dcc32 Error] HistoricalStockData.pas(298): E2033 Types of actual and formal var parameters must be identical'. As I see they are already identical.
Question number 2: Should I modify my source code with the each new delphi version?
Thanks.
Answer
The reason TIdBytes was a simple alias for TBytes in earlier Indy 10 releases was primarily for compatibility with SysUtils.TEncoding, which uses TBytes. Indy's TIdTextEncoding type used to be a simple alias for SysUtils.TEncoding in D2009+, so TIdBytes needed to be a simple alias for TBytes to match.
However, TBytes caused quite a bit of trouble for Indy in XE3, mainly because of RTTI problems with Generics (TBytes is a simple alias for TArray<Byte> in recent Delphi releases). So, Indy 10.6 re-designed TIdTextEncoding to no longer rely on SysUtils.TEncoding at all (there were other reasons as well for doing so), which then allowed TIdBytes to change into its own array type in order to avoid the XE3 issues moving forward.
On the other hand, you were passing a TBytes where a TIdBytes was expected, so that is bad programming on your part for not following Indy's defined interface in the first place. All of Indy 10's byte-based operations, including ReadBytes(), have always operated on TIdBytes only. The fact that TIdBytes silently mapped to TBytes was an implementation detail that you should not have relied on in your code. Indy 10 expects TIdBytes, so use TIdBytes, then you would not have compiler errors about incompatible types.