How to Check if 3 Variables are equal or not equal to each other in Swift 5?

Question

i am currently working on an App that needs to compare three Variables with each other.

Rules for Comparison: The result should only be true if: All three variables are equal OR All three variables are different

My first idea was something like this, but I hope there is a more elegant solution for this:

if (value1 == value2 && value2 == value3) || (value1 != value2 && value2 != value3 && value3 != value1) {
    // True
} else {
    // False
}

I would be really happy if someone of you can think of a more elegant solution and share it with me. Thanks for your help in advance!

Answer 1

If your values are also Hashable you can use a Set . Given the fact that a Set discards duplicate values, you can simplify your check to something like this:

let valuesArray = [value1, value2, value3]
let valuesSet = Set(valuesArray)

if valuesSet.count == 1 || valuesSet.count == valuesArray.count {
    // True
} else {
    // False
}

Answer 2

For a one-off, that's not too bad.

The more "general" solution is kind of messy, because it needs to track 2 different boolean variables, and handle empty collections correctly.

extension Sequence where Element: Equatable {
    func classifyElementEquality() -> (allEqual: Bool, allUnequal: Bool) {
        var iterator = self.makeIterator()
        
        guard let first = iterator.next() else {
            return (true, true) // all empty
        }
        
        return AnyIterator(iterator)
            .reduce(into: (allEqual: true, allUnequal: true)) { acc, element in
                if first == element {
                    acc.allUnequal = false
                } else {
                    acc.allEqual = false
                }
            }
    }
}

let (value1, value2, value3) = (1, 2, 3)
let result = [value1, value2, value3].classifyElementEquality()

if result.allEqual || result.allUnequal {
    print("They're either all equal, or all unequal")
} else {
    print("Some of them are different")
}

It can get a bit simpler if this algorithm targets Collection insteaad of Sequence , because accessing the first element is easier without needing to manually manage an iterator.

extension Collection where Element: Equatable {
    func classifyElementEquality() -> (allEqual: Bool, allUnequal: Bool) {
        guard let first = self.first else {
            return (true, true) // all empty
        }
        
        return self
            .dropFirst()
            .reduce(into: (allEqual: true, allUnequal: true)) { acc, element in
                if first == element {
                    acc.allUnequal = false
                } else {
                    acc.allEqual = false
                }
            }
    }
}