Yeah, I agree that whatever forward reference model we'll end up with
down the road, the conditional thing I was doing in Thrift will probably
be illegal there. Fortunately, that one's easy to remove – it was just
to avoid adding a »useless« empty field, the value of which is
questionable anyway.
Also, I hope that I didn't come across too grumpy – if so, it was
certainly not intended, as I know that I'm not exactly sticking to
well-trodden ground in some parts of the Thrift implementation. It's
just that I already ended up tracking down seven issues during what I
hoped would be a bit of hassle-free pre-release testing, and currently,
I'm working on reducing another strange, possibly related bug…
David
On 11 Apr 2012, at 2:35, Walter Bright wrote:
I mostly agree with you, and apologize for the trouble it caused you.
The fact that it worked at all before was a fluke, caused by
incomplete checking by the compiler, and that incomplete checking
caused numerous other problems.
Allowing forward references in general is a very tricky problem in the
situation of circular definitions. The strategy that dmd originally
followed was to do things in lexical order, and dang the consequences.
The more advanced strategy dmd has been migrating to is to allow
circular references as long as there is enough information about the
partially analyzed type to break the cycle. For example, sometimes
only the size of a struct is required. Therefore, dmd requires only
that the members of the struct that contribute to its size are
analyzed - the other members need not be.
In your case, you had a static if turning on and adding members by
checking a condition that must check all the members. This cannot
possibly work. I spent a lot of type trying to figure out a way that
the cycle could be legitimately broken, but could not.
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