[Swift] ExpressibleByStringLiteral, CustomStringConvertible

https://developer.apple.com/documentation/swift/expressiblebystringliteral

ExpressibleByStringLiteral - Swift Standard Library | Apple Developer Documentation

Overview

The String and StaticString types conform to the ExpressibleByStringLiteralprotocol. You can initialize a variable or constant of either of these types using a string literal of any length.

Conforming to ExpressibleByStringLiteral

To add ExpressibleByStringLiteral conformance to your custom type, implement the required initializer.

 

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https://developer.apple.com/documentation/swift/customstringconvertible

CustomStringConvertible - Swift Standard Library | Apple Developer Documentation

Overview

Types that conform to the CustomStringConvertible protocol can provide their own representation to be used when converting an instance to a string. The String(describing:) initializer is the preferred way to convert an instance of any type to a string. If the passed instance conforms to CustomStringConvertible, the String(describing:) initializer and the print(_:) function use the instance’s custom description property.

Accessing a type’s description property directly or using CustomStringConvertible as a generic constraint is discouraged.

Conforming to the CustomStringConvertible Protocol

Add CustomStringConvertible conformance to your custom types by defining a description property.

For example, this custom Point struct uses the default representation supplied by the standard library:

 

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Example

enum CompassPoint {
    case north
    case south
	case custom(String)
}

extension CompassPoint: ExpressibleByStringLiteral {
	init(stringLiteral value: String) {
        switch value {
        case "north":
            self = .north
        case "south":
            self = .south
		default:
        	self = .custom(value)
		}
	}
}

extension CompassPoint: CustomStringConvertible {
	public var description: String {
        switch self {
        case .north:
	        return "north"
        case .south:
        	return "south"
        case .custom(let type):
            return type
        }
    }
}