Subscripts in Swift

Subscripts provide a convenient way to access the elements of a collection, list, or sequence directly by index. Whether you’re dealing with arrays, dictionaries, or custom types, subscripts allow you to set and retrieve values without needing separate methods for each operation.

What is a subscript?

Subscripts are shortcuts for accessing the member elements of a collection, list, or sequence. They are used to set and retrieve values without needing separate methods for each operation.

Use Case of a subscript

extension Collection {
    // Support collection[safe: number]
    subscript (safe index: Index) -> Element? {
        return indices.contains(index) ? self[index] : nil
    }

    // Support collection[safe: number, default: "some default value"]
    subscript (safe index: Index, default value: Element) -> Element {
        return indices.contains(index) ? self[index] : value
    }
}

let pokemon = ["Pikachu", "Lugia", "Dragonite", "Mewtwo"]

pokemon[10] // will crash 💥
pokemon[safe: 10] // returns nil
pokemon[safe: 10, default: "Pikachu"] // returns Pikachu.

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Conclusion

Subscripts provide a convenient way to access the elements of a collection, list, or sequence directly by index. Whether you’re dealing with arrays, dictionaries, or custom types, subscripts allow you to set and retrieve values without needing separate methods for each operation.

Resources:

https://docs.swift.org/swift-book/documentation/the-swift-programming-language/subscripts/