FourCharCode+String.swift

import Foundation

/**
 Set FourCharCode/OSType using a String.
 
 Examples:
 let test: FourCharCode = "420v"
 let test2 = FourCharCode("420f")
 print(test.string, test2.string)
*/
extension FourCharCode: ExpressibleByStringLiteral {
    
    public init(stringLiteral value: StringLiteralType) {
        var code: FourCharCode = 0
        // Value has to consist of 4 printable ASCII characters, e.g. '420v'.
        // Note: This implementation does not enforce printable range (32-126)
        if value.count == 4 && value.utf8.count == 4 {
            for byte in value.utf8 {
                code = code << 8 + FourCharCode(byte)
            }
        }
        else {
            print("FourCharCode: Can't initialize with '\(value)', only printable ASCII allowed. Setting to '????'.")
            code = 0x3F3F3F3F // = '????'
        }
        self = code
    }
    
    public init(extendedGraphemeClusterLiteral value: String) {
        self = FourCharCode(stringLiteral: value)
    }
    
    public init(unicodeScalarLiteral value: String) {
        self = FourCharCode(stringLiteral: value)
    }
    
    public init(_ value: String) {
        self = FourCharCode(stringLiteral: value)
    }
    
    public var string: String {
        let bytes: [CChar] = [
            CChar((self >> 24) & 0xff),
            CChar((self >> 16) & 0xff),
            CChar((self >> 8) & 0xff),
            CChar(self & 0xff),
            0
        ]
        let result = String(cString: bytes)
        let characterSet = CharacterSet.whitespaces
        return result.trimmingCharacters(in: characterSet)
    }
}

Usage example:

var formatDesc: CMFormatDescription? = nil
CMFormatDescriptionCreate(allocator: nil, mediaType: kCMMediaType_Text, mediaSubType: FourCharCode(stringLiteral: "tx3g"), extensions: nil, formatDescriptionOut: &formatDesc)