Add collection strawman #1 #820
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Can assume P#T <: Q#T if P <: Q. This follows from the rules how we expand # to existentials.
Some subtype tests should not instantiate type variables, in particular those having to do with & and |.
withMode sets the whole mode, nit an individual bits. This was used wrongly in several places. Make this less of a trap by renaming withMode -> withModeBits.
Logging while printing messes up the recursion counts.
make successive underlying values an iterator (so that we do not run into a stackoverflow in case of cycles).
Avoid redundant computations when already in printing mode.
We had problems printing constraints which are ill-formed, because the basic operations & , | cause exceptions themselves. toString serves as a fallback if show does not work.
Cases like these (in fact one of the operads was a type variable the other its underlying polyparam) arose in pos/overloads.scala and caused deep subtype recursions.
Checking whether two alternatives are the same should not unify them by instantiating type variables.
Overall goal: Push backtracking deeper into the tree.
Iter2.scala fails with 6 errors, but succeeds once lubs and glbs do not try to unify under invariant type constructors.
There is a diff, but a minor one. Instead of
(T? >: Int <: Int)
we get
(T? = Int) after pickling.
According to the new subtyping rules,
T <: U ==> T#X <: U#X and T#x <: U#x
Therefore type maps should treat the prefix of a named type
covariantly.
This compiles only after the changes in this branch.
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Based on #805.