Hi, While working on bindings to the GObject type system, I could not help noticing the amount of boilerplate I ended up with trying to represent OOP-style class inheritance:
https://gist.github.com/mzabaluev/02202b4a8819687094be#file-foreign-inheritance-and-cast-rs-L18 The trait reform and UFCS should take away much of the pain, but a really nice solution would be a way to annotate `impl A for InstA` as auto-derivable or "inheritable", so that any type implementing `Inherit<InstA>` (here, a proposed special standard trait) would automatically get its own implementation of `A` in terms of the upcast provided by `Inherit`. Furthermore, that implicit trait implementation would in turn be "inheritable", so that any indirect subclass would implement `A`, and any other inheritable traits in the chain of its parents, for free. Not all traits would be available for such treatment; dependencies on static properties of Self a la `fn new() -> Self` would preclude it. But the traits that a classic OOP hierarchy lends itself to, should be just what the doctor ordered. Note also how the default implementations of the inheritable trait methods are amenable to tail call elimination. If the compiler itself would generate those shims, it could just emit inherited impls' vtable entries as trampolines to the base impl, and similarly apply the tail-call hinting during static monomorphization. Does the above make sense, or am I getting the whole subject wrong and there is (or will soon be) a better Rust idiomatic for that? Care for an RFC pull request? Mikhail
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