How to check if an Element is in an Array in Swift

Swift Array has two methods to check whether an element is in an array.

1. contains(_:)
2. contains(where:)

contains

The contains(_:) method returns true if an array contains the given element.

This method only supports an array in which Element conforms to the Equatable protocol.

Here is an example where we use contains with an array of strings. String conforms to the Equatable protocol, so we can use the contains method here.

let names = ["John", "Alice", "Bob"]
        
// 1
print(names.contains("John"))
// true

// 2
print(names.contains("john"))
// false

// 3
print(names.contains("Sarun"))
// false

1 The names array contains "John".
2 The names array doesn't contains "john". Uppercase and lowercase matter here.
3 The names array doesn't contains "Sarun".

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contains(where:)

If the element in an array doesn't conform to Equatable or you want to specify a custom compare logic, you can do it with contains(where:).

The contains(where:) returns true if an element satisfies the given predicate block.

The Element doesn't need to conform anything to use the contains(where:) method.

The logic that indicates equality is in the passing predicate closure. You return true to tell the passed element is in the array.

func contains(where predicate: (Self.Element) throws -> Bool) rethrows -> Bool

As an example, we create a new Contact struct. It doesn't conform to the Equatable protocol.

struct Contact {
    let name: String
}

In this example, we check whether contacts contain a contact with the name "John".

let contacts: [Contact] = [
    Contact(name: "John"),
    Contact(name: "Alice"),
    Contact(name: "Bob")
]

let containJohn = contacts.contains { contact in
    return contact.name == "John"
}
print(containJohn)
// true