Relaxin the PVP with regards to adding instances

Ian Lynagh igloo at
Tue Sep 11 20:58:29 CEST 2012

On Tue, Sep 11, 2012 at 02:11:36PM -0400, Edward Kmett wrote:
> I often add instances for my own classes to my own types, and the need for
> a major version bump can ripple through 20+ packages and then out into 3rd
> party packages.

If you're adding the instance at the same time as adding either the type
or the class, then a major bump shouldn't be needed.

However, if you often find that you need to add an instance for an
existing class+type, then isn't it plausible that the authors of these
3rd party packages would find they need the instances first, so add
orphan instances? In which case they would break if you add the instance
without bumping the major version.

A "no orphan instance" rule could work, but note that not only could you
not use orphan instances yourself, but you also couldn't use any
packages that contain orphan instances. I think that to make that work
in practice we'd have to make orphan instances an error, unless either
the type or the class is in the current package.


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