Swift protocols don't enforce the `throws` keyword on methods? Is this a bug or a feature? Paste this code into a new Xcode 8.3.2 playground...

ThrowOrDontWhatevs.swift

//: Playground - noun: a place where people can play

import Foundation

protocol CharacteristicValue {
    
    func characteristicValue() throws -> Data
}

extension String: CharacteristicValue {
    
    // Why does this compile without "throws"?
    // Shouldn't it complain that it does not conform to the protocol?
    func characteristicValue() -> Data {
        return self.data(using: .utf8)!
    }
}

let testData = "TEST DATA".characteristicValue()

let result = String(data: testData, encoding: .utf8)

// Now lets use the protocol in a structure
// and access the String object through it.

struct Test {
    
    let charValue: CharacteristicValue
    
    init(charValue: CharacteristicValue) {
        self.charValue = charValue
    }
}

let test = Test(charValue: "TEST DATA")
let str = test.charValue

// The compiler requires the "try?" here even though
// the specific implementation does not throw.
let foo = try? test.charValue.characteristicValue()