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Swift 4 allows multiple protocols to be called at once with the help of protocol composition.
In Swift, a protocol defines a blueprint of methods or properties that can then be adopted by classes (or any other types). We use the protocol keyword to define a protocol. For example, protocol Greet { // blueprint of a property var name: String { get } // blueprint of a method func message() }
You can create objects from classes, whereas protocols are just type definitions. Try to think of protocols as being abstract definitions, whereas classes and structs are real things you can create.
Protocols allow you to group similar methods, functions, and properties. Swift lets you specify these interface guarantees on class , struct , and enum types. Only class types can use base classes and inheritance from a protocol.
How to list all classes implementing a given protocol in Swift?
Say we have an example:
protocol Animal { func speak() } class Cat:Animal { func speak() { print("meow") } } class Dog: Animal { func speak() { print("Av Av!") } } class Horse: Animal { func speak() { print("Hurrrr") } } Here is my current (not compilable) approach:
func getClassesImplementingProtocol(p: Protocol) -> [AnyClass] { let classes = objc_getClassList() var ret = [AnyClass]() for cls in classes { if class_conformsToProtocol(cls, p) { ret.append(cls) } } return ret } func objc_getClassList() -> [AnyClass] { let expectedClassCount = objc_getClassList(nil, 0) let allClasses = UnsafeMutablePointer<AnyClass?>.alloc(Int(expectedClassCount)) let autoreleasingAllClasses = AutoreleasingUnsafeMutablePointer<AnyClass?>(allClasses) let actualClassCount:Int32 = objc_getClassList(autoreleasingAllClasses, expectedClassCount) var classes = [AnyClass]() for i in 0 ..< actualClassCount { if let currentClass: AnyClass = allClasses[Int(i)] { classes.append(currentClass) } } allClasses.dealloc(Int(expectedClassCount)) return classes } But when calling either
getClassesImplementingProtocol(Animal.Protocol) or
getClassesImplementingProtocol(Animal) or
getClassesImplementingProtocol(Animal.self)
results in Xcode error: cannot convert value of type (Animal.Protocol).Type to expected argument type 'Protocol'.
Did anyone manage get this working?
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