https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170116/030522.html

I think assigning to ‘self’ should be permitted in all convenience initializers, even initializers defined directly classes, without the protocol extension trick. Also, we should lower this more efficiently than we do today, without creating a self ‘carcass’ that is allocated and immediately freed, to be replaced by the ‘real’ self.