[swift-dev] [SE-0143] Dynamic casting for conditional conformances

Brent Royal-Gordon brent at architechies.com
Sun Dec 10 18:47:34 CST 2017

> On Dec 5, 2017, at 2:28 PM, Douglas Gregor via swift-dev <swift-dev at swift.org> wrote:
> To perform that mapping from a mangled type in a conditional requirement to type metadata, we effectively need an operation to take a mangled type name and turn it into a type metadata pointer. This is something we could surface in the Swift standard library/runtime as, e.g.,
> func type(named: String) -> Any.Type?
> to take a mangled type name and try to get the type metadata for it. From there, one can query protocol conformances that (say) allow one to construct instances of the arbitrarily-named type. Think of it as NSClassFromString for any type in the Swift language, including specializations of generic types.

It's worth noting here that the standard library already provides a limited `_typeByName(_:)` function for Corelibs Foundation to use. That function will presumably become part of the ABI unless we design a public version in Swift 5.

Brent Royal-Gordon

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