LVGUtilities

A set of basic utilities written in Swift, used mainly as a dependency for other projects like LVGSwiftSimpleSoundServices.

Motivation

This framework is a set of utilities that I developed while working on Swift wrappers for the various Audio Toolbox APIs. Working with C language APIs in Swift is awkward, and these utilities make it less so.

The CBridgingFunctions file contains a set of functions for converting class objects to and from const void C pointers. For example, the function toPointer(_:) replaces this awkward bit of code…

// object is an `AnyObject` of some type
let pointer = UnsafeMutablePointer(Unmanaged.passUnretained(object).toOpaque())

…with this slightly less awkward line:

let pointer = toPointer(object)

The toPointer(_:) and fromPointer functions cast objects to and from UnsafeMutablePointer<Void>, respectively, without retaining or consuming refrences to the object. If you want to retain a reference, use toPointerRetain(_:) or fromPointerConsume(_:) instead.

The remaining protocols and type extensions are handy for working with Audio Toolbox’s many OSStatus error codes and API-defined constants.

For example, kAudioServicesUnsupportedPropertyError is an OSStatus error code that may be returned by a function from the System Sound Services API. It has a 4-character string translation of 'pty?'. The CodedErrorType protocol can be used as a helpful structure in converting these error codes into standard Swift ErrorTypes. In LVGSwiftSystemSoundServices, the kAudioServicesUnsupportedPropertyError gets translated to an enum case .UnsupportedProperty. When thrown, it has a nice printable description:

System Sound Services Error: Unsupported property.
    Message: A helpful message that can provide information about the context from where the error was thrown.
    Code: 285229988 ('pty?')

CodedErrorType has a static method check(_:message:) that checks an OSStatus error code and throws an error if it does not equal 0, with a message to provide information about the context from where the error was thrown.

The CodedPropertyType is similar, but for API constants that represent API properties. For example, System Sound Services uses the UInt32 constant kAudioServicesPropertyIsUISound to refer to whether or not the sound honors the user’s decision to turn off sound effects. In LVGSwiftSystemSoundServices this is translated to an enum case .IsUISound.

Both CodedErrorType and CodedPropertyType include a property called code which returns the constant defined by the API. The also both conform to RawRepresentable, where the rawValue is, by default the same as the code property.

There are also extensions on OSStatus (which is just a typealias for Int32) and UInt32, that convert them to a four-character string through their codeString property, where each character is represented by one byte in the four-byte integer type. Strings exactly four unicode scalars in length can also be converted to either an Int32 or an UInt32 value.

Requirements

• OS X 10.10 or later
• iOS 8.0 or later

Installation

LVGUtilities is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod "LVGUtilities"

Author

letvargo, [email protected]

License

LVGUtilities is available under the MIT license. See the LICENSE file for more info.