Generic type array do not take empty array as input

Question

import Foundation


func insertionSort<T where T: Comparable>(var items:[T])-> [T] {

    for (index, _) in items.enumerate().dropFirst() {
        var j = index

        while ((j > 0) && (items[j] < items[j-1])) {
            swap(&items[j], &items[j-1])
            j = j-1
        }
    }
    return items
}


// Test the function
insertionSort([]) // Generic type array is not taking empty array

When I am trying to call insertionSort with empty array, I get

Cannot invoke 'insertionSort' with an argument list of type '([_])'

I am not able to figure out how to fix this.

@Lu_ `var` required for `items` because I am making changes in the array. — Rahul, Jul 22 '16 at 13:15
let tab: [String] = [] let a = insertionSort(tab) swift need declared array type, your sorting is working if it is swift array — Lu_, Jul 22 '16 at 13:17

score 2 · Accepted Answer · answered Jul 22 '16 at 14:50

To call generic functions in Swift, Swift needs to be able to infer the generic parameters.

One way giving the type information to Swift, is using an intermediate variable. (Like noted in Lu_'s comment.)

let arr: [Int] = []
let result = insertionSort(arr)

Another way is using as.

let result = insertionSort([] as [Int])

(Remember, var parameter does not modify the actual argument. It just makes a mutable copy, but does not write it back to the original argument. Swift 3 removed var parameters, as it's so confusing. You may need to assign the return value of the function to a variable.)

Generic type array do not take empty array as input

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