[fpc-pascal] Incompleteness of current fix for #22860

[Jonas Maebe]

JC Chu wrote on Thu, 13 Sep 2012:

> Regarding bug #22860 on the inability to define enumeration members
> using expressions containing previously defined members of the same
> type, the current fix does not provide a complete solution.
>
> The current fix won’t allow for valid declarations such as TYPE
> TMyEnum = (meA, meB = 1 + meA) and TYPE TMyEnum = (meA, meB = meA xor
> meA).

Thanks, I'll fix that.

> Forbidding all of those enumeration-related overloads, however, will
> undo much of what the relaxation patch was intended for.

As I think I mentioned in the original thread, I was never a very big  
fan of that relaxation because of unforeseen side effects.

> The compiler should expect an integer-typed constant expression after
> ‘=’, with a weakened type checking that takes as Ord(x) each
> enumeration member x in the expression, where x must belong to the
> enumeration type being declared, and must appear before the member
> it’s used to define.

I think one of the prime requirements to get readable code is that a  
compilable expression always means the same. Changing the meaning of  
"enum + int" or vice versa depending on whether you're in a type  
definition or in regular code following an overloaded operator goes  
completely against that principle.

Of course, a programmer can circumvent that by defining a particular  
operator in multiple units with different meanings, but at least as  
far as natively supported operators are concerned we can ensure that  
this principle is respected.


Jonas