When to use `protocol` and `protocol: class` in Swift?

swift, swift-protocols

Solution

Swift 4 version

`AnyObject` added to a protocol definition like this

protocol FilterViewControllerDelegate: AnyObject  {
    func didSearch(parameters:[String: String]?)
}

means that only a class will be able to conform to that protocol.

So given this

protocol FilterViewControllerDelegate: AnyObject  {
    func didSearch(parameters:[String: String]?)
}

You will be able to write this

class Foo: FilterViewControllerDelegate {
    func didSearch(parameters:[String: String]?) { }
}

but NOT this

struct Foo: FilterViewControllerDelegate {
    func didSearch(parameters:[String: String]?) { }
}

Swift 3 version

`:class` added to a protocol definition like this

protocol FilterViewControllerDelegate: class  {
    func didSearch(Parameters:[String: String]?)
}

means that only a class will be able to conform to that protocol.

So given this

protocol FilterViewControllerDelegate: class  {
    func didSearch(Parameters:[String: String]?)
}

You will be able to write this

class Foo: FilterViewControllerDelegate {
    func didSearch(Parameters:[String: String]?) { }
}

but NOT this

struct Foo: FilterViewControllerDelegate {
    func didSearch(Parameters:[String: String]?) { }
}

Problem

I have setup a protocol to send some information back to the previous VC. I define it like this: ``` protocol FilterViewControllerDelegate: class { func didSearch(Parameters:[String: String]?) } ``` But what is the difference when using: ``` protocol FilterViewControllerDelegate { func didSearch(Parameters:[String: String]?) } ``` And when should I use a `: class` protocol?

Original source