Add documentation for type class derivation #7063
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I'll merge this when it goes green unless anyone has any objections. |
| type MirroredType | ||
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| /** the type of the elements of the mirrored type */ | ||
| type MirroedElemTypes |
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| type MirroedElemTypes | |
| type MirroredElemTypes |
| def fromProduct(p: scala.Product): MirroredMonoType | ||
| } | ||
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| trait Sum extends Mirror { self => |
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| trait Sum extends Mirror { self => | |
| trait Sum extends Mirror { |
| // Mirror for Tree | ||
| Mirror.Sum { | ||
| type MirroredType = Tree | ||
| type MirroredElemTypes[T] = (Branch[T], Leaf[T]) |
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I’m confused that MirroredElemTypes now takes a type parameter, even though in the definition of Mirror it is *-kinded. Is this valid?
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MirroredElemTypes is defined in subtypes of Mirror where the appropriate kind is known. The definition I showed as a member of Mirror is illustrative rather than actual ... I guess I should at least mention this at that point, but I didn't want to complicate things. One option would be to define these types in Mirror with an AnyKind bound ... do you think that would be preferable to deferring the definitions?
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One option would be to define these types in
Mirrorwith anAnyKindbound ... do you think that would be preferable to deferring the definitions?
Maybe it’s not needed. Your explanation made it clear. We can probably just add somewhere that the shown Mirror definition is not the actual one, but a simplified version.
| ### Mirrors | ||
| with the instances for children in hand the `derived` method uses an `inline match` to dispatch to methods which can | ||
| construct instances for either sums or products (2). Note that because `derived` is `inline` the match will be | ||
| resolved at compile-time and only the left-hand side of the matching case will be inlined into the generated code with |
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| resolved at compile-time and only the left-hand side of the matching case will be inlined into the generated code with | |
| resolved at compile-time and only the right-hand side of the matching case will be inlined into the generated code with |
Needs elaboration, but it's up to date, and the running example is reasonably simple given that it's low-level, and works as expected.