When I try to execute the code below, I get the following error
error: cannot convert value of type 'X' to specified type 'X'
Doesn't swift support inheritance with generics? Is there a workaround for this?
class Parent{ }
class Child:Parent{ }
class X<T>{
var name: String?
}
var test:X<Parent> = X<Child>() //Compiler Error
In Swift, generics are invariant, e.g. any X<A> will never be assignable to X<B>, regardless of the inheritence relationship between A and B.
Nevertheless, there are some exceptions to this rule, regarding Arrays and Optionals (and mabye some other types):
var array2:[Parent] = [Child]()
// same as:
var array1:Array<Parent> = Array<Child>()
var opt1:Parent? = Child()
// same as:
var opt2:Optional<Parent> = Optional<Child>(Child())
These will compile (since Swift 3) - but these a special cases treated by some hard-coded rules of the the compiler.
P, make classX<T>conform toP. Then usePas return type for your method. You can then return X<Child> as well as X<Parent> from within your method.extension X: P {…}