Fix #7458: Refine typevar interpolation #7562
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If there are several type variables to instantiate in an interpolation call, instantiate first those type variables that do not tighten the constraint for other instantiatable type variables. The following code from i7458.scala requires this new scheme to compile. ``` type Tr[+V1, +O1 <: V1] def [V2, O2 <: V2](tr: Tr[V2, O2]) sl: Tr[V2, O2] = ??? def as[V3, O3 <: V3](tr: Tr[V3, O3]) : Tr[V3, O3] = tr.sl ``` Interestingly, adding `()` to the parameter list of `sl` makes the problem disappear even without the fix. The reason is that in this case interpolation is suspended to a later point since expressions of method type are not interpolated.
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Nov 18, 2019
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| if fromBelow then constraint.isLess(following.origin, tvar.origin) | ||
| else constraint.isLess(following.origin, tvar.origin) |
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These two lines are the same, I assume one is supposed to have its parameters flipped ? (Incidentally this is why I like to always put a new line before each branch of an if/else, this makes this sort of things easier to spot :)).
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Glad you spotted this!
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If there are several type variables to instantiate in an interpolation call,
instantiate first those type variables that do not tighten the constraint for
other instantiatable type variables.
The following code from i7458.scala requires this new scheme to compile.
Interestingly, adding
()to the parameter list ofslmakesthe problem disappear even without the fix. The reason is that in
this case interpolation is suspended to a later point since expressions of
method type are not interpolated.