Hi Ben, The reason to include init?<T : BinaryInteger>(exactly:T) as a requirement for the Arithmetic (now Number) protocol was that it already refines ExpressibleByIntegerLiteral, so it would be quite weird to *not* allow explicit initialization.
Generic conversion to floating point types is not covered by this proposal, but is somewhat related: https://github.com/apple/swift/blob/master/stdlib/public/core/FloatingPoint.swift.gyb#L257 <https://github.com/apple/swift/blob/master/stdlib/public/core/FloatingPoint.swift.gyb#L257> https://github.com/apple/swift/blob/master/stdlib/public/core/FloatingPoint.swift.gyb#L1588 <https://github.com/apple/swift/blob/master/stdlib/public/core/FloatingPoint.swift.gyb#L1588> There are a few unimplemented (but planned) initializers on FloatingPoint and BinaryFloatingPoint that would make this happen. If and when those are implemented, you would be able to write the version of numericCast<I : BinaryInteger, F : BinaryFloatingPoint>() using those. Hope this answers your question. Max > On Jan 17, 2017, at 9:43 AM, Ben Rimmington <m...@benrimmington.com> wrote: > > <https://gist.github.com/moiseev/62ffe3c91b66866fdebf6f3fcc7cad8c> > > public protocol Arithmetic { > init?<T : BinaryInteger>(exactly source: T) > } > > public protocol BinaryInteger : Arithmetic { > init?<T : FloatingPoint>(exactly source: T) > } > > Should the `init?(exactly:)` initializers belong to the same protocol? > Would this allow generic conversions between integer and floating-point types? > For example, a failable `numericCast` function. > > -- Ben >
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