How to make generics in collection type constraint?

Question

I have been trying to extract non-nil values from the String array. Like below. But, my senior wants it to be able to extract non-nil values from other type

Answer 1

The easiest approach is using flatMap as kennytm suggested, but if you absolutely want to know how to create such a method using generics, one approach would be to create a global method that takes in the collection as a parameter:

public func getNonNil>(collection: C) -> [T] {
    return collection.filter({$0 != nil}).map({$0!})
}

let x: [String?] = ["Er", "Err", nil, "errr"]

print(getNonNil(x)) // returns ["Er", "Err", "errr"]