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Date: Tue, 23 May 2017 21:25:32 +0200
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Subject: Parameter type widening RFC
From: rasmus@mindplay.dk (Rasmus Schultz)

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This parameter type widening RFC, I didn't know about, but I have a remark.

The feature, as implemented, will allow accidental omission of type-hints,
will it not?

Previously, the implements keyword guaranteed a correctly type-hinted
implementation - it's now possible to (purposefully, obviously, in certain
rare cases) omit type-hints by accident, making the implements keyword much
less (or not any) of a guarantee that the interface is implemented
correctly.

The addition of an explicit "mixed" or "any" pseudo-type would have made
this possible, without losing the guarantee that the implements keyword
used to provide - that is, it would have been possible to have this feature
for the few cases where it's useful, without affecting safety in the
majority of other cases where it's not.

I feel like this feature takes a pretty dangerous shortcut by simply
removing a constraint check that we used to have - in favor of supporting a
few rare cases, we removed a guarantee that interfaces and the
implements-keyword has always provided.

Those rare cases could have been supported in a safe manner by introducing
a "mixed" or "any" type, which would have made the use of this feature
explicit - which would have removed the risk of accidental omission of
type-hints in the majority of cases.

The RFC page doesn't link to any discussion, and the Github thread was shut
down after some negative remarks.

I didn't see a discussion or a vote here on internals - did I miss
something? Where or how did this get discussed and passed? Are these
discussions happening somewhere else besides internals now?

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