Comparing two [String: Any] dictionaries in Swift 4

Question

I have two dictionaries that work as text attributes of type [String: Any] and in order to toggle ON or OFF the desired attributes I need to check if two dictionaries are the same.

I tried the following:

let current = inputTextView.typingAttributes

let undo = current.elementsEqual(attributes, by: { (arg0, arg1) -> Bool in
    return ((arg0.key == arg1.key) && (arg0.value == arg1.value))
})

But on the second evaluation I get the error:

Binary operator '==' cannot be applied to two 'Any' operands

What's the best approach here to compare two dictionaries of type [String: Any] ??

Thank you

Answer 1

Details

• Xcode Version 10.3 (10G8), Swift 5

Solution

func areEqual (_ left: Any, _ right: Any) -> Bool {
    if  type(of: left) == type(of: right) &&
        String(describing: left) == String(describing: right) { return true }
    if let left = left as? [Any], let right = right as? [Any] { return left == right }
    if let left = left as? [AnyHashable: Any], let right = right as? [AnyHashable: Any] { return left == right }
    return false
}

extension Array where Element: Any {
    static func != (left: [Element], right: [Element]) -> Bool { return !(left == right) }
    static func == (left: [Element], right: [Element]) -> Bool {
        if left.count != right.count { return false }
        var right = right
        loop: for leftValue in left {
            for (rightIndex, rightValue) in right.enumerated() where areEqual(leftValue, rightValue) {
                right.remove(at: rightIndex)
                continue loop
            }
            return false
        }
        return true
    }
}
extension Dictionary where Value: Any {
    static func != (left: [Key : Value], right: [Key : Value]) -> Bool { return !(left == right) }
    static func == (left: [Key : Value], right: [Key : Value]) -> Bool {
        if left.count != right.count { return false }
        for element in left {
            guard   let rightValue = right[element.key],
                areEqual(rightValue, element.value) else { return false }
        }
        return true
    }
}

Usage

let comparisonResult = ["key1": 1, 2: "Value2"] == ["key1": ["key2":2]]     // false
print("!!!! \(comparisonResult)")

Some tests

func test(dict1: [AnyHashable : Any], dict2:  [AnyHashable : Any]) {
    print("========================")
    print("dict1: \(dict1)")
    print("dict2: \(dict2)")
    print("are\(dict1 == dict2 ? " " : " not ")equal")
}

test(dict1: ["key1": 1, 2: "Value2"],
     dict2: ["key1": 1, 2: "Value2"])

test(dict1: ["key1": 1, 2: "Value2"],
     dict2: ["key1": 1])

test(dict1: [2: "Value2"],
     dict2: ["key1": 1])

test(dict1: ["1": 1],
     dict2: [1: 1])

test(dict1: [1: 2],
     dict2: [1: 3])

test(dict1: ["key1": [1,2,3,4]],
     dict2: ["key1": [1,2,3,4]])

test(dict1: ["key1": [1,2,3,4]],
     dict2: ["key1": [2,1,3,4]])

test(dict1: ["key1": [1,2,3,4]],
     dict2: ["key1": [2,1,3]])

test(dict1: ["key1": [1,2,3,4]],
     dict2: ["key1": [1,2,3,"4"]])

test(dict1: ["key1": ["key2":2]],
     dict2: ["key1": ["key2":2]])

test(dict1: ["key1": ["key2":2]],
     dict2: ["key1": ["key2":3]])

test(dict1: ["key1": ["key2":2]],
     dict2: ["key1": ["key2":3]])

Tests results

========================
dict1: [AnyHashable("key1"): 1, AnyHashable(2): "Value2"]
dict2: [AnyHashable("key1"): 1, AnyHashable(2): "Value2"]
are equal
========================
dict1: [AnyHashable("key1"): 1, AnyHashable(2): "Value2"]
dict2: [AnyHashable("key1"): 1]
are not equal
========================
dict1: [AnyHashable(2): "Value2"]
dict2: [AnyHashable("key1"): 1]
are not equal
========================
dict1: [AnyHashable("1"): 1]
dict2: [AnyHashable(1): 1]
are not equal
========================
dict1: [AnyHashable(1): 2]
dict2: [AnyHashable(1): 3]
are not equal
========================
dict1: [AnyHashable("key1"): [1, 2, 3, 4]]
dict2: [AnyHashable("key1"): [1, 2, 3, 4]]
are equal
========================
dict1: [AnyHashable("key1"): [1, 2, 3, 4]]
dict2: [AnyHashable("key1"): [2, 1, 3, 4]]
are equal
========================
dict1: [AnyHashable("key1"): [1, 2, 3, 4]]
dict2: [AnyHashable("key1"): [2, 1, 3]]
are not equal
========================
dict1: [AnyHashable("key1"): [1, 2, 3, 4]]
dict2: [AnyHashable("key1"): [1, 2, 3, "4"]]
are not equal
========================
dict1: [AnyHashable("key1"): ["key2": 2]]
dict2: [AnyHashable("key1"): ["key2": 2]]
are equal
========================
dict1: [AnyHashable("key1"): ["key2": 2]]
dict2: [AnyHashable("key1"): ["key2": 3]]
are not equal
========================
dict1: [AnyHashable("key1"): ["key2": 2]]
dict2: [AnyHashable("key1"): ["key2": 3]]
are not equal

Answer 2

Any does not conform to Equatable protocol. It is a must-have for a type if the == operator will be used. Therefore, you need to compare your Any objects using a function that takes a type parameter as mentioned in this answer:

func isEqual<T: Equatable>(type: T.Type, a: Any, b: Any) -> Bool? {
    guard let a = a as? T, let b = b as? T else { return nil }
    return a == b
}

However, to use this function, you should know the exact type of each value in typingAttributes. You can achieve this using the Mirror struct as follows:

let lilAny: Any = "What's my type? :("
print(Mirror(reflecting: lilAny).subjectType) // String