Sets in Delphi XE are not working the same way they worked in D7

Question

I had this constants in a Delphi 7 program. They are not compiling under Delphi XE.

TYPE
  TSingleChar= AnsiChar;

CONST
  noData: TSingleChar= '.';
  Ambiguity= ['x'];
  DNA_Ambig= ['x', noData]+ Ambiguity;

[DCC Error] E2026 Constant expression expected.

1. What was changed in XE that my old code does not compile?
2. I suppose that the code, as it is, is interpreted as Unicode. Am I correct?

Iveson

I assume you "sanitized" the code too much before posting it; What you posted compiles without error on Delphi 7, Delphi 2010 and Delphi XE. – Tablet

I just tried it in Delphi 2009 (which is Unicode), and it compiles fine. – Looseleaf

@Altar: Are you sure that Ambiguity really is declared as const? Are you sure that you do exactly like above in your actual code? – Looseleaf

About your point (2), characters in sets are actually interpreted as AnsiChar, not Unicode; Try compiling this and look at the error message: Ambiguity = ['Б','В','Г','Ґ','Д','Ђ'] – Tablet

There is an interesting point here though. Why is Delphi incapable of recognising a typed constant as being constant? Is it a hangover from that horrid oxymoron, the writeable typed constant? – Enculturation

@Altar: I'd suggest you open your test unit and press Ctrl-O-O to insert all compiler options at the top. So you can be sure everybody tests the same. – Amitie

@Downvoters, probably time to revoke the downvotes. Maybe even upvote. – Tablet

@Cosmin - Are you sure this is any different in D7? If not the question title can still be a reason for a downvote. – Squalene

@Sertac, it works absolutely the same in Delphi 7, 2010 and XE. Altar should also edit the title! – Tablet

-1. Reported code hasn't compiled in any version. – Cyclosis

Answer 1

"Fix" it like this:

TYPE
  TSingleChar= AnsiChar;

CONST
  Const_noData = '.';
  noData: TSingleChar= Const_noData;
  Ambiguity= ['x'];
  DNA_Ambig= ['x', Const_noData]+ Ambiguity;

The Const_noData is a true const as far as the compiler's concerned, allowing you to initialize both noData and DNA_Ambig using it. And you still respect the DRY principle, ie, there's only one definition for noData, the Const_noData.

Tablet

This is just so depressing to me. I long for some future nirvana when constants really are, you know, constant. – Enculturation

Thanks. That solved the issue. (Well the code now looks pretty ugly since I have lots of constants and now I have two declarations for each of them... but I guess I have to accept this). – Iveson

You could avoid having two declarations, Altar, but removing the typed constants. – Cyclosis

Answer 2

const
  Ambiguity:  TAnsiCharSet = ['B', 'D', 'H'];
  Ambiguity2: TAnsiCharSet = ['C', 'c', 't'] + Ambiguity;

does not work.

const
  Ambiguity = ['B', 'D', 'H'];
  Ambiguity2 = ['C', 'c', 't'] + Ambiguity;

does work. Typed constants aren't really constants at all...

(Notice that the issue has nothing to do with ambiguity. It is about what is considered a constant and what is not.)

Looseleaf