warning: 'characters' is deprecated: Please use String or Substring directly

Swift 4 vs Swift 3 examples:

let myString = "test"

for char in myString.characters {print(char) } // Swift 3
for char in myString { print(char) } // Swift 4

let length = myString.characters.count // Swift 3
let length = myString.count // Swift 4

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One of the most common cases for manipulating strings is with JSON responses. In this example I created an extension in my watch app to drop the last (n) characters of a Bitcoin JSON object.

Swift 3:

func dropLast(_ n: Int = 0) -> String {
    return String(characters.dropLast(n))

Xcode 9.1 Error Message:

'characters' is deprecated: Please use String or Substring directly

Xcode is telling us to use the string variable or method directly.

Swift 4:

func dropLast(_ n: Int = 0) -> String {
    return String(dropLast(n))
    }

Complete Extension:

extension String {
    func dropLast(_ n: Int = 0) -> String {
        return String(dropLast(n))
    }

    var dropLast: String {
        return dropLast()
    }
}

Call:

print("rate:\(response.USDRate)")
let literalMarketPrice = response.USDRate.dropLast(2)
print("literal market price: \(literalMarketPrice)")

Console:

//rate:7,101.0888 //JSON float
//literal market price: 7,101.08 // JSON string literal

Additional Examples:

print("Spell has \(invisibleSpellName.count) characters.")

return String(dropLast(n))

return String(removeLast(n))

Documentation:

You'll often be using common methods such as dropLast() or removeLast() or count so here is the explicit Apple documentation for each method.

droplast()

removelast()

counting characters

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Use this characters because String stopped being a collection in Swift 2.0. However this is still valid code in Swift 4 but is no longer necessary now that String is a Collection again.

For example a Swift 4 String now has a direct count property that gives the character count:

// Swift 4
let spString = "Stack"
spString.count           // 5

Examples for String and SubString.

String

Swift 4 String now directly get Element that gives the first character of String: (string.characters.first)

let spString = "Stack"
let firstElement = spString.first   //S

SubString

Using SubString get first character.

let spstring = "Welcome"
let indexStartOfText = spstring.index(spstring.startIndex, offsetBy: 1)
let sub = spstring.substring(to: indexStartOfText)
print(sub) //W

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That warning is just a top of the iceberg, there were a loot of string changes, strings are again a collection of characters, but we got soemthing new and cool, subStrings :)

This is a great read about this: https://useyourloaf.com/blog/updating-strings-for-swift-4/

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Just remove characters For example:

stringValue.characters.count to stringValue.count

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You can also use this code for dictionary grouping without using { $0.characters.first! }.

let cities = ["Shanghai": 24_256_800, "Karachi": 23_500_000, "Beijing": 21_516_000, "Seoul": 9_995_000]
let groupedCities = Dictionary(grouping: cities.keys) { $0.first! }
print(groupedCities)

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func validatePhoneNumber(number:String) -> Bool{
    if number.count < 10. //deprecated ->(number.characters.count)
    {
        return false;
    }else{
        return true;
    }
}

You use directly .count and characters is deprecated.

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