During a recent discussion with several D folks, several people, including Walter told ma that the situation with multiple alias this and alias this in classes was hopelessly broken. I suggested it needed to be either fixed or removed.
However, during this discussion, I took the fact it was hopelessly broken for granted. But it doesn't appear to me that this is obvious. Can someone familiar with the topic care to explain or point me to a link where this case was made already?
On an asside, I implemented both multiple alias this and alias this for classes in SDC. Because these feature were never completed in DMD, I had to extrapolate to figure out what the semantic should be, and this is what I came up with.
1/ Alias this is used in two contextes: casts and identifier resolution.
2/ For struct, it just follow the expected rule for cast and resolution, if these rule succeed, then nothing more happen. If they fail, then the operation is repeated again with all the declared alias this. If the number of valid result is 1 and exactly 1, then it is used. If the number of valid result is 0 or greater than 1, then an error is emitted.
3/ For classes, lookups ignore alias this and walk up the parent stack, still ignoring any alias this. If that fails, then all the alias this from this class and its parent are run at once, and if the number of valid result is 1, then this is fine, if it is 0 or greater than 1, then an error is emitted. The same is done for casts.
I think this semantic is reasonable. But I have to say I did not put a ton of though into it, so maybe there is a big fatal flaw I'm overlooking.