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SOLVED: Question: about 'sorted(closure)`

Forums > 100 Days of SwiftUI
@boat  

Hi When Paul demonstrating closure , he used sorted (by: code of closures).

https://www.hackingwithswift.com/quick-start/beginners/how-to-use-trailing-closures-and-shorthand-syntax

let team = ["Gloria", "Suzanne", "Piper", "Tiffany", "Tasha"]

let captainFirstTeam = team.sorted(by: { (name1: String, name2: String) -> Bool in
    if name1 == "Suzanne" {
        return true
    } else if name2 == "Suzanne" {
        return false
    }

    return name1 < name2
})

print(captainFirstTeam)

Quetions: Does this mean sorted() is taking in the returned Bool generated by the closure as a parameter ?

How do I know what type of parameters sorted are meant to take in ? Or I could just pass in any type of parameters to sorted ?

Thank you in advance,

Boat

4      

@roosterboy  HWS+

sorted(by:) gives you two elements from the sequence and you return a Bool indicating if those two elements are in the correct order. The implementation of sorted(by:) then uses that result to sort the sequence.

You don't really need to know what type of parameters to pass in to sorted(by:); Swift takes care of that for you by passing it whatever type the sequence's Element is. (i.e., if your sequence is [String], the closure gets two Strings; if the sequence is [Int], the closure gets two Ints, etc) You also don't need to indicate the closure's return type.

let captainFirstTeam = team.sorted(by: { name1, name2 in
    return name1 < name2
})

Heck, you don't even need to name the parameters:

let captainFirstTeam = team.sorted(by: { 
    return $0 < $1
})

The closure syntax can be reduced even more than that, but that might be a good place to stop for now.

So, basically, if you look at sorted(by:)'s signature in the documentation:

func sorted(by areInIncreasingOrder: (Element, Element) throws -> Bool) rethrows -> [Element]

you'll see that the closure takes two items that are whatever type the sequence's Elements are and returns a Bool.

5      

@boat  

Thank you @roosterboy !

3      

@dsnovaes  

It helped me a lot to understand the "name1" and "name2" parameters when I put 'print' commands to see the action happening:

func captainFirstSorted(name1: String, name2: String) -> Bool {
    let captain = "Suzanne"
    if name1 == captain {
        print("\(name1) is being compared to \(name2), and \(name1) should come first")
        return true
    } else if name2 == captain {
        print("\(name1) should not be before \(name2)")
        return false
    }
    print("\(captain) is not being compared, so just sort \(name1) and \(name2)")
    return name1 < name2
}

5      

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