Argument labels do not match any availble overloads - swift

I'm trying to create an anagram tester, and I'm pretty sure the code I have should work, but I'm getting an error 'Argument labels '(_:)' do not match any available overloads' I've looked at the other posts regarding the same error, but I'm still not sure what this means or how to fix it.
var anagram1 : String!
var anagram2 : String!
var failure : Bool = false
var counter : Int = 0
print("Please enter first word: ")
anagram1 = readLine()
print("Please enter Second word: ")
anagram2 = readLine()
if anagram1.count == anagram2.count {
for i in anagram1.characters{
if (!failure){
failure = true
for y in anagram2.characters {
counter += 1
if i == y {
failure = false
anagram2.remove(at: String.Index(counter)) // error here
}
}
}
else {
print("these words are not anagrams")
break;
}
}
if (!failure) {
print("these words ARE anagrams")
}
}
else{
print ("these words aren't even the same length you fucking nonce")
}

To answer your first question: the error message Argument labels '(_:)' do not match any available overloads means that you've given a function parameter names or types that don't match anything Swift knows about.
The compiler is also trying to tell you what parameters to look at. '(_:)' says that you're calling a function with an unlabeled parameter. (That means a value without any parameter name. A common example of a function that would look like this is print("something"). In Swift documentation, this would look like print(_:).
Finally, overloads are ways to call a function with different information. Again using the print function as an example, you can call it multiple ways. A couple of the most common overloads would be:
// print something, followed by a newline character
print("something")
// print something, but stay on the same line
// (end with an empty string instead of the default newline character)
print("something", terminator: "")
Documented, these might look like print(_:) and print(_:, terminator:).
Note: these are broken down for explanation. The actual Swift documentation shows func print(_: Any..., separator: String, terminator: String) which covers a number of different overloads!
Looking at the line where the error occurs, you see a function call and an initializer (which is essentially a function). Documented, the way you've entered the parameters, the functions would look like: remove(at:) and String.Index(_:).
String.Index(_:) matches the parameters of the error message, so that's where your error is. There is no overload of the String.Index initializer that takes an unnamed parameter.
To fix this error, you need to find the correct way to create a String.Index parameter for the remove(at:) function. One way might be to try something like this:
for y in anagram2.characters.enumerated() {
// `y` now represents a `tuple`: (offset: Int, element: Character)
// so, you don't need `counter` anymore; use `offset` instead
if i == y.element { //`i` is a Character, so it can compare to `element`
...
let yIndex: String.Index = anagram2.index(anagram2.startIndex, offsetBy: y.offset)
anagram2.remove(at: yIndex)
...
}
}
However, there are other issues with your code that will cause further errors.
For one, you're looping through a string (anagram2) and trying to change it at the same time - not a good thing to do.
Good luck to you in solving the anagram problem!

Thanks for the help Leo but I found a way of doing it :)
if anagram1.count == anagram2.count {
for i in anagram1.characters{
if (!failure){
counter = -1
failure = true
for y in anagram2.characters {
counter += 1
if i == y {
failure = false
if counter < anagram2.count {
anagram2.remove(at: (anagram2.index(anagram2.startIndex, offsetBy: counter)))
break;
}
}
}
}

Related

No exact matches in call to subscript , If I use forEach, does not work

Please check the attached code below.
Why Pattern raise Error? , "No exact matches in call to subscript"
What is the difference between A and B?
This is the text import from the console.
3
Everest 8849
K2 8611
Kangchenjunga 8586
This is code
struct Mountain {
let name: String
let height: Int
}
func highestmountain() {
var mtList = [Mountain]()
let N = Int(readLine()!)!
(0..<N)
.forEach { _ in
/* Pattern A */
readLine()!
.split(separator: " ")
.forEach {
mtList.append(Mountain(name: "\($0[0])", height: Int("\($0[1])")!)) // Error: No exact matches in call to subscript
}
/* Pattern B */
let reads = readLine()!
.split(separator: " ")
mtList.append(Mountain(name: "\(reads[0])", height: Int("\(reads[1])")!)) // works!
}
}
In Pattern A, you're using split(" ") which creates an array of Strings (or, more specifically, String.SubSequence), and then you call forEach on that array.
forEach calls the attached closure for each item in the array. So, with your second input line, for example, on the first forEach, $0 will be "Everest" and on the second call, it'll be 8849. However, in your code, you're attempting to get $0[0], but $0 is not an array -- it's a single String.SubSequence. Thus the error about the subscript.
Your second approach (Pattern B) works because reads is an Array of String.SubSequence, so using a subscript (ie the [0]) works.
Unrelated to your question, but it's worth noting that using subscripts like [1] will fail and crash the app if you haven't first checked to make sure that the array has enough items in it. Force unwrapping with a ! (like you do with Int(...)!) can also cause crashes.

How to use the binary operator "%" with user input "readLine()"?

I have been asked to write a code using If/Else statements. The code is supposed to ask the user to enter a number and then print "This number is even" if the number is even, and print "This number is odd" if the number is odd. To do this, I am using the binary operator "%" in order to find out whether the number imputed is even or odd. The problem is that I keep getting this error that says: "error: binary operator '%' cannot be applied to operands of type 'String?' and 'Int' if a % 2 == 0". I do not know how to make the user input become an Int value instead of the default String so that the binary operator will work.
I have been suggested to try Type Casting, but nothing I do seems to be working.
print("This code will inform you whether the number you input is odd or even.")
print("Please enter a number of your choice.")
var a = readLine()
if a % 2 == 0 {
print("This number is even.")
}
else {
print("This number is odd.")
}
I expect the user to be able to input a number and the computer to tell the user whether the number is odd or even.
readLine() returns an optional string. To unwrap optional there are couple of options in swift, I guess its three options there. One is force unwrapping, second is optional chaining and third is by guard statement. Here in the option below I have used optional chaining to unwrap optional string returned by redLine(). Try this:
if let typed = readLine() {
if let num = Int(typed) {
if num % 2 == 0 {
print("This number is even.")
}
else {
print("This number is odd.")
}
}
} else {
print("Please enter a valid number")
}

Binary operator '==' cannot be applied to operands of type '[String]' and 'String

I am new to coding and I needed some help with answering this challenge.
Instructions:
// Given the two arrays below, write a function that takes a String as an input parameter and returns a Boolean value. The function should return true if the String input is in either array and it should return false if the String input is in neither array.
//
// Examples:
// Call your function and pass in the String "cat" as the input. Your function should return true
// Call your function and pass in the String "cow" as the input. Your function should return false
let array1 = ["dog", "cat", "bird", "pig"]
let array2 = ["turtle", "snake", "lizard", "shark"]
// Write your function below:
Here is where I have written my function:
func test(Animal:String){
let list = array1 + array2
for animal in list {
if list == animal {
print("true")
} else {
print("false")
}
}
}
test(Animal: "dog")
The error I am getting is:
Binary operator '==' cannot be applied to operands of type '[String]' and 'String under the if statement.
Help if you can and I apologize in advance if this is not formatted correctly.
Thanks!
Just a tip, in the future you should try adding a more descriptive question title, that is super vague and could mean anything.
Anyways your issue is with the line:
if list == animal {
The error you got is quite specific and tells you exactly what's going wrong. [String] is an array of strings while String is just a single item. So when you write for animal in list your taking one animal in that list at a time.
Comparing an animal to a list is not allowed. They are not the same type ([String] and String are different types, as the compiler error told you). You can only compare variables of the same type. So in your case a list (String array aka [String]) to a another list, or an animal (String) to an animal.
Now what you want to do is see if a string you got is in either array. There's actually a built in method in arrays that lets you do exactly this: .contains
func test(animal:String){
let list = array1 + array2
if list.contains(animal) {
print("true")
} else {
print("false")
}
}
or if you want to be extra concise with some good code you can try
func test(animal:String){
let list = array1 + array2
print(list.contains(animal)) // will be false if it doesn't so prints false, true if it does so prints true.
}
And another side note.. You want to be very careful doing an if else inside of a for loop where both the if and the else return. You shouldn't be making decisions after looking at only ONE element.
Because typically you want to check EVERY value before printing false, but when you have an if else, you'll return/print after checking ONLY the first value.
if you wanted to do it your way (no built in methods, iterating through the array) you would want to do something like this:
func test(animal:String){
let list = array1 + array2
for candidate in list {
if animal == candidate { // there's a match! we can return true
print("true ")
return // return says to exit the function since we no longer need to keep going this is appropriate
}
} // for loop ends
// we only return false once the ENTIRE for loop has run, because we know if it did exist, we would never get to this point in the code
// this part only runs once EVERY item has been checked and none were a match
print("false")
}
And finally as bilal says, never start variable names with capital letters. Typically capital letters mean its a type (like String). You'll notice I renamed Animal -> animal for you in my examples

How to handle initial nil value for reduce functions

I would like to learn and use more functional programming in Swift. So, I've been trying various things in playground. I don't understand Reduce, though. The basic textbook examples work, but I can't get my head around this problem.
I have an array of strings called "toDoItems". I would like to get the longest string in this array. What is the best practice for handling the initial nil value in such cases? I think this probably happens often. I thought of writing a custom function and use it.
func optionalMax(maxSofar: Int?, newElement: Int) -> Int {
if let definiteMaxSofar = maxSofar {
return max(definiteMaxSofar, newElement)
}
return newElement
}
// Just testing - nums is an array of Ints. Works.
var maxValueOfInts = nums.reduce(0) { optionalMax($0, $1) }
// ERROR: cannot invoke 'reduce' with an argument list of type ‘(nil, (_,_)->_)'
var longestOfStrings = toDoItems.reduce(nil) { optionalMax(count($0), count($1)) }
It might just be that Swift does not automatically infer the type of your initial value. Try making it clear by explicitly declaring it:
var longestOfStrings = toDoItems.reduce(nil as Int?) { optionalMax($0, count($1)) }
By the way notice that I do not count on $0 (your accumulator) since it is not a String but an optional Int Int?
Generally to avoid confusion reading the code later, I explicitly label the accumulator as a and the element coming in from the serie as x:
var longestOfStrings = toDoItems.reduce(nil as Int?) { a, x in optionalMax(a, count(x)) }
This way should be clearer than $0 and $1 in code when the accumulator or the single element are used.
Hope this helps
Initialise it with an empty string "" rather than nil. Or you could even initialise it with the first element of the array, but an empty string seems better.
Second go at this after writing some wrong code, this will return the longest string if you are happy with an empty string being returned for an empty array:
toDoItems.reduce("") { count($0) > count($1) ? $0 : $1 }
Or if you want nil, use
toDoItems.reduce(nil as String?) { count($0!) > count($1) ? $0 : $1 }
The problem is that the compiler cannot infer the types you are using for your seed and accumulator closure if you seed with nil, and you also need to get the optional type correct when using the optional string as $0.

swift, optional unwrapping, reversing if condition

Let's say I have function which returns optional. nil if error and value if success:
func foo() -> Bar? { ... }
I can use following code to work with this function:
let fooResultOpt = foo()
if let fooResult = fooResultOpt {
// continue correct operations here
} else {
// handle error
}
However there are few problems with this approach for any non-trivial code:
Error handling performed in the end and it's easy to miss something. It's much better, when error handling code follows function call.
Correct operations code is indented by one level. If we have another function to call, we have to indent one more time.
With C one usually could write something like this:
Bar *fooResult = foo();
if (fooResult == null) {
// handle error and return
}
// continue correct operations here
I found two ways to achieve similar code style with Swift, but I don't like either.
let fooResultOpt = foo()
if fooResult == nil {
// handle error and return
}
// use fooResultOpt! from here
let fooResult = fooResultOpt! // or define another variable
If I'll write "!" everywhere, it just looks bad for my taste. I could introduce another variable, but that doesn't look good either. Ideally I would like to see the following:
if !let fooResult = foo() {
// handle error and return
}
// fooResult has Bar type and can be used in the top level
Did I miss something in the specification or is there some another way to write good looking Swift code?
Your assumptions are correct—there isn't a "negated if-let" syntax in Swift.
I suspect one reason for that might be grammar integrity. Throughout Swift (and commonly in other C-inspired languages), if you have a statement that can bind local symbols (i.e. name new variables and give them values) and that can have a block body (e.g. if, while, for), those bindings are scoped to said block. Letting a block statement bind symbols to its enclosing scope instead would be inconsistent.
It's still a reasonable thing to think about, though — I'd recommend filing a bug and seeing what Apple does about it.
This is what pattern matching is all about, and is the tool meant for this job:
let x: String? = "Yes"
switch x {
case .Some(let value):
println("I have a value: \(value)")
case .None:
println("I'm empty")
}
The if-let form is just a convenience for when you don't need both legs.
If what you are writing is a set of functions performing the same sequence of transformation, such as when processing a result returned by a REST call (check for response not nil, check status, check for app/server error, parse response, etc.), what I would do is create a pipeline that at each steps transforms the input data, and at the end returns either nil or a transformed result of a certain type.
I chose the >>> custom operator, that visually indicates the data flow, but of course feel free to choose your own:
infix operator >>> { associativity left }
func >>> <T, V> (params: T?, next: T -> V?) -> V? {
if let params = params {
return next(params)
}
return nil
}
The operator is a function that receives as input a value of a certain type, and a closure that transforms the value into a value of another type. If the value is not nil, the function invokes the closure, passing the value, and returns its return value. If the value is nil, then the operator returns nil.
An example is probably needed, so let's suppose I have an array of integers, and I want to perform the following operations in sequence:
sum all elements of the array
calculate the power of 2
divide by 5 and return the integer part and the remainder
sum the above 2 numbers together
These are the 4 functions:
func sumArray(array: [Int]?) -> Int? {
if let array = array {
return array.reduce(0, combine: +)
}
return nil
}
func powerOf2(num: Int?) -> Int? {
if let num = num {
return num * num
}
return nil
}
func module5(num: Int?) -> (Int, Int)? {
if let num = num {
return (num / 5, num % 5)
}
return nil
}
func sum(params: (num1: Int, num2: Int)?) -> Int? {
if let params = params {
return params.num1 + params.num2
}
return nil
}
and this is how I would use:
let res: Int? = [1, 2, 3] >>> sumArray >>> powerOf2 >>> module5 >>> sum
The result of this expression is either nil or a value of the type as defined in the last function of the pipeline, which in the above example is an Int.
If you need to do better error handling, you can define an enum like this:
enum Result<T> {
case Value(T)
case Error(MyErrorType)
}
and replace all optionals in the above functions with Result<T>, returning Result.Error() instead of nil.
I've found a way that looks better than alternatives, but it uses language features in unrecommended way.
Example using code from the question:
let fooResult: Bar! = foo();
if fooResult == nil {
// handle error and return
}
// continue correct operations here
fooResult might be used as normal variable and it's not needed to use "?" or "!" suffixes.
Apple documentation says:
Implicitly unwrapped optionals are useful when an optional’s value is confirmed to exist immediately after the optional is first defined and can definitely be assumed to exist at every point thereafter. The primary use of implicitly unwrapped optionals in Swift is during class initialization, as described in Unowned References and Implicitly Unwrapped Optional Properties.
How about the following:
func foo(i:Int) ->Int? {
switch i {
case 0: return 0
case 1: return 1
default: return nil
}
}
var error:Int {
println("Error")
return 99
}
for i in 0...2 {
var bob:Int = foo(i) ?? error
println("\(i) produces \(bob)")
}
Results in the following output:
0 produces 0
1 produces 1
Error
2 produces 99