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

[Douglas Gregor]

> On Dec 12, 2017, at 2:29 PM, Jordan Rose <jordan_rose at apple.com> wrote:
> 
> 
> 
>> On Dec 12, 2017, at 14:15, Douglas Gregor via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>> 
>> 
>> 
>>> On Dec 10, 2017, at 4:47 PM, Brent Royal-Gordon <brent at architechies.com <mailto:brent at architechies.com>> wrote:
>>> 
>>>> On Dec 5, 2017, at 2:28 PM, Douglas Gregor via swift-dev <swift-dev at swift.org <mailto: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.
>> 
>> 
>> Woah. That’s kinda awful… it parses “Foo.Bar” as a class name and looks for class Bar in module Foo.
> 
> Needed to implement NSCoding on Linux. They did limit it to "Foo.Bar" at least, deliberately excluding anything more complicated.

Makes sense. A type(named:) would serve their use case better, of course.

	- Doug


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-dev/attachments/20171212/8e8ecbb8/attachment.html>