"Use of undeclared type " error when iterating over an array of Type

Question

Given an array containing instances of several SubClasses (all having the same SuperClass), I want to check if all the elements of another array of required subClass Types are represented by the instances.

I came up with what I think is a valid solution, but I'm plagued by the error: Use of undeclared type 'requiredType' in the closure for requiredTypes.allSatisfy { ... }

class MyClass { }

class SubClass1: MyClass { }
class SubSubClass1: SubClass1 { }
class SubClass2: MyClass { }
class SubClass3: MyClass { }

let requiredTypes = [SubClass1.self, SubClass2.self]

let instances = [SubSubClass1(), SubClass2()]

let meetsRequirements = requiredTypes.allSatisfy { (requiredType) -> Bool in
    return instances.map({$0 is requiredType}).contains(true)
}

This is a code smell. I suspect what you're trying to do would be better achieved by formalizing it in a protocol. — Alexander
– Alexander, Commented Feb 7, 2019 at 18:42

Sulthan · Accepted Answer · 2019-02-07 18:49:16Z

4

is operator requires a type that is known at compile-time. You cannot use a variable there.

One possibility is to use type(of:), e.g.:

let meetsRequirements = requiredTypes.allSatisfy { requiredType in 
    instances.contains { type(of: $0) == requiredType }
}

Although that will be a problem with SubSubClass1.

If your classes inherit from NSObject, you can use:

let meetsRequirements = requiredTypes.allSatisfy { requiredType in 
    instances.contains { $0.isKind(of: requiredType) }
}

Checking whether a class inherits from a type which is stored in a variable is not currently supported in Swift. Usually it's a code smell.

edited Feb 7, 2019 at 18:49

answered Feb 7, 2019 at 18:39

Sulthan

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