Non-parametric derived instances now lazy vals #6905
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Previously all derived instances would be compiled as given defs, which have caching logic added, where possible, in CacheAliasImplicits. These caches are unsynchronized, which is a reasonable default in circumstances where the progammer has the option to manually insert a lazy val or some other form of synchronization. That option isn't available for derived instances, however, because these givens aren't written explicitly. In this case the more appropriate default is to compile non-parametric derived instances as given lazy vals.
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@odersky this is ready for review now. |
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If #7006 gets in, this PR will no longer be necessary. |
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Happy to close this one :-) |
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Currently all derived instances would be compiled as given defs, which have caching logic added, where possible, in
CacheAliasImplicits. These caches are unsynchronized, which is a reasonable default in circumstances where the programmer has the option to manually insert a lazy val or some other form of synchronization.That option isn't available for derived instances, however, because these givens aren't written explicitly. In this case the more appropriate default is to compile non-parametric derived instances as given lazy vals.
This PR makes that change. Unfortunately the tests aren't all that convincing because an identity test isn't sufficient to distinguish between a lazy val and a def with unsynchronized caching logic. Suggestions for a better approach to the test would be very welcome.