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cmd/go2go: nonsensical recursive type compiles #40884

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benjaminjkraft opened this issue Aug 19, 2020 · 1 comment
Closed

cmd/go2go: nonsensical recursive type compiles #40884

benjaminjkraft opened this issue Aug 19, 2020 · 1 comment
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@benjaminjkraft
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benjaminjkraft commented Aug 19, 2020 •
edited

Here are two types (playground):

type A[type X] interface{ a(X) }
type B[type X A[B]] interface{ b(X) }

The type A[B] is semantically invalid; B needs to be instantiated. But this seems to be allowed currently.

In fact if we modify A a bit we can even supposedly implement B (playground):

type A[type X] interface{ b(B[X]) }
type B[type X A[B]] interface{ b(X) }
type S struct{}
func (_ S) b(A[int]) {}
var _ B[A[int]] = S{}
@ianlancetaylor ianlancetaylor added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Aug 19, 2020
@ianlancetaylor ianlancetaylor added this to the Unreleased milestone Aug 19, 2020
@griesemer
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This code now reports a proper cycle error (playground). Closing.

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