Indy Changed from Indy10
http://stackoverflow.com/questions/16339656/delphi-xe4-indy-compatibility-issue-between-tbytes-and-tidbytes
http://stackoverflow.com/questions/19402374/delphi-xe3-indy-compatibility-issue-between-tbytes-and-tidbytes
http://stackoverflow.com/questions/18849053/how-should-i-adapt-my-code-for-compatibility-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.
Answers:
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.
share|improve this answer
edited May 2 '13 at 17:18
answered May 2 '13 at 16:24
Remy Lebeau
149k882162
1
Libraries that invent their own types instead of using equivalent RTL types just leads to ghettoisation. How can we write code that uses Indy and its byte array and interacts with another library using its byte array? – David Heffernan May 4 '13 at 0:31
First tell Embarcadero to stop breaking their own products when they make RTL changes. TBytes used to be a simple dynamic array (like TIdBytes is now). It worked great with RTTI, Object Inspector, compiler, etc. Then they switched TBytes to TArray<Byte> and broke all of that (bad Generics RTTI, bad C++ codegen, etc). Also remember that Indy supports multiple languages, and TArray<T> works differently in C++ than in Delphi. So there were multiple reasons for making TIdBytes go back to a simple dynamic array. I didn't make the change lightly, and even Embarcadero recommended I do it at the time. – Remy Lebeau May 4 '13 at 3:13
OK, I'm sure you had good reason to change. It feels all wrong to me that in 2013 there's still debate over how to handle byte arrays. The "right" solution, assuming everything could be made to work, would be for all code to use TArray<T> directly and so enjoy the special type compatibility rules for generic types. So in an ideal world there would be no TBytes, no TIdBytes, and libraries could happily co-exist and interact smoothly. – David Heffernan May 4 '13 at 14:52
The following two declarations are not the same, even though they appear to be. They're not assignment compatible, even though they're both based on array of string.
type
TStringArrayOne = array of string;
TStringArrayTwo = array of string;
var
AVar1, AVar2: TStringArrayOne;
AVar3, AVar4: TStringArrayTwo;
begin
AVar1 := TStringArrayOne.Create('a', 'b', 'c'); // Compiles
AVar2 := TStringArrayTwo.Create('a', 'b', 'c'); // Won't compile
AVar3 := TStringArrayTwo.Create('a', 'b', 'c'); // Compiles
AVar4 := TStringArrayOne.Create('a', 'b', 'c'); // Won't compile
end;
So TBytes and TIdBytes are not the same type, even if they're both defined as being array of Byte.
With regard to your question 2: It's a common problem with some third-party code. Indy in particular is known for making changes that breaks backward compatibility because they decide to reorganize or rewrite things between versions. Indy 10 was a major change from Indy 9, IIRC, and pretty much required a rewrite of most code that used it if you updated to the later version of Indy (even without updating Delphi at the same time). If you don't want to deal with those changes, you might want to look at using a more stable IP communications package. There are several available that are also free, open source packages.
In Indy 10.5.9 the type TIdBytes was defined differently depending on the presence of an existing TBytes type - see unit IdGlobal:
{$IFDEF HAS_TBytes}
TIdBytes = TBytes;
{$ELSE}
TIdBytes = array of Byte;
{$ENDIF}
In Indy 10.6 (included in XE4), the declaration changed to unconditionally
TIdBytes = array of Byte;
which means that starting with Indy 10.6, IdGlobal.TIdBytes is different from SysUtils.TBytes.
The second question is hard to answer, it is more a question of your priorities - other libraries are not immune against changes either, for example to improve performance or type-safety. Also changes in the Delphi language can always affect existing code.
Question2:
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I am having the same problem as mentioned in "Delphi XE4 Indy compatibility issue between TBytes and TidBytes ", i.e. compatibility issues between TBytes(Delphi RTL) and TIdBytes(Indy) datatypes when compiling with the Delphi XE4. The source of my problem is that the code is not exactly according to Indy's interface and some of functions use TBytes, instead of TIdBytes, when calling native Indy IO procedures.
So I was wondering what will the best fix be?
As I see it there are two approaches:
1.Refactor all functions in the project to use TIdBytes rather than TBytes.
2.Implement a TBytesToTidBytes conversion procedure (converts the TBytes to TIdBytes) and call that procedure prior to making the mentioned native Indy calls.
Which of the approaches is better/best? Do you have any other ideas on how I can do that?
FYI: The project I am trying to configure with the XE4 is available online on sourceforge : http://sourceforge.net/projects/indy10clieservr/?source=directory
The suggested conversion procedure should be something like:
procedure TBytesToTIdBytes(const Input:TBytes, var Output: TIdBytes)
var
i,L : Integer;
allocate : Boolean;
begin
L := Length(Input);
if(Length(Output) <> L) then
begin
SetLength(Output,L);
end;
if(L > 0) then
move(Pointer(Input)^,Pointer(Output)^,L);
end;
Answer:
TBytes and TIdBytes are both implemented as dynamic arrays, they are simply declared differently. The "politically correct" solution is to make a copy of the bytes. But that can waste memory for large arrays. A simpler solution is to use a typecast so you can utilize the array's internal reference count, eg:
type
PIdBytes = ^TIdBytes;
var
B1: TBytes;
B2: TIdBytes;
begin
B1 := ...;
B2 := PIdBytes(@B1)^;
end;
Or simply:
var
B1: TBytes;
B2: TIdBytes;
begin
B1 := ...;
B2 := TIdBytes(B1);
end;
Both types are not the same at implementation level, in newer Delphi versions (TBytes is a simple alias for TArray<Byte> in recent Delphi releases).
So I guess you can use such a procedure:
procedure TBytesToTIdBytes(const Input: TBytes; var Output: TIdBytes);
var L: integer;
begin
L := Length(Input);
SetLength(Output,L);
move(Input[0],Output[0],L);
end;
Here move() is faster than a loop.