Swift Language Generics Constraining Generic Placeholder Types
Example
It is possible to force the type parameters of a generic class to implement a protocol, for example, Equatable
class MyGenericClass<Type: Equatable>{
var value: Type
init(value: Type){
self.value = value
}
func getValue() -> Type{
return self.value
}
func valueEquals(anotherValue: Type) -> Bool{
return self.value == anotherValue
}
}Whenever we create a new MyGenericClass, the type parameter has to implement the Equatable protocol (ensuring the type parameter can be compared to another variable of the same type using ==)
let myFloatGeneric = MyGenericClass<Double>(value: 2.71828) // valid
let myStringGeneric = MyGenericClass<String>(value: "My String") // valid
// "Type [Int] does not conform to protocol 'Equatable'"
let myInvalidGeneric = MyGenericClass<[Int]>(value: [2])
let myIntGeneric = MyGenericClass<Int>(value: 72)
print(myIntGeneric.valueEquals(72)) // true
print(myIntGeneric.valueEquals(-274)) // false
// "Cannot convert value of type 'String' to expected argument type 'Int'"
print(myIntGeneric.valueEquals("My String"))
