Swift 4 Encodable doesn't work with protocols
| Originator: | aufflick | ||
| Number: | rdar://33866425 | Date Originated: | Aug 13 2017 |
| Status: | Open | Resolved: | |
| Product: | Developer Tools | Product Version: | Xcode 9 b5 9M202q |
| Classification: | It's serious man | Reproducible: | Always |
Summary:
If you have a struct adopt Encodable, and one of it's properties has a protocol type (which supports Encodable), the swift compiler will complain that the protocol does not support Encodable.
Steps to Reproduce:
Write this amazing code into a playground in Xcode 8 b5:
import Foundation
protocol FooProtocol : Encodable {
var foo: String { get }
}
struct Bar : Encodable {
var bar: FooProtocol
}
Expected Results:
Successful compilation
Observed Results:
Playground execution failed:
error: EncodablePlayground.playground:1:8: error: type 'Bar' does not conform to protocol 'Encodable'
struct Bar : Encodable {
^
EncodablePlayground.playground:2:9: note: cannot automatically synthesize 'Encodable' because 'FooProtocol' does not conform to 'Encodable'
var bar: FooProtocol
^
Comments
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Further, explicitly adding a concrete encode function to the protocol does not help. The following also fails:
import Foundation
protocol SomeBanana : Encodable { var oops: String { get } } struct B2 : SomeBanana { var oops: String { return "After you B1" } } struct B1 : SomeBanana { var oops: String { return "After you B2" } } extension SomeBanana { func encode(to encoder: Encoder) throws { var container = encoder.singleValueContainer() try container.encode(oops) } }
struct StripedPyjamas : Encodable { var wornBy: SomeBanana }