Create Property Wrapper in Swift

In Swift, property wrappers are a language feature that allows you to wrap a piece of code around a property, in order to add additional behavior or functionality to that property. Property wrappers are defined using the @ symbol, followed by the name of the property wrapper.

Here’s an example of a simple property wrapper called Trimmed that trims leading and trailing whitespace from a string:

@propertyWrapper
struct Trimmed {
    private(set) var wrappedValue: String

    init(wrappedValue: String) {
        self.wrappedValue = wrappedValue.trimmingCharacters(in: .whitespaces)
    }
}

You can use this property wrapper by applying it to a property like this:

Property wrappers are a useful tool for adding functionality to properties in a concise and reusable way. They are often used for things like value validation, data formatting, and thread synchronization.

Test property wrapper

To test above property wrapper:

import XCTest

class TrimmedTests: XCTestCase {
    func testTrimmed() {
        let person = Person(name: "  John Smith   ")
        XCTAssertEqual(person.name, "John Smith")
    }
    
    struct MockPerson {
        @Trimmed var name: String
    }
}

Originally published at https://needone.app on December 19, 2022.

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