CustomPlaygroundDisplayConvertible

Playground logging can generate, at a minimum, a structured description of any type. If you want to provide a custom description of your type to be logged in place of the default description, conform to the CustomPlaygroundDisplayConvertible protocol.

Playground logging generates a richer, more specialized description of core types. For example, the contents of a String are logged, as are the components of an NSColor or UIColor. The current playground logging implementation logs specialized descriptions of at least the following types:

• String and NSString

• Int, UInt, and the other standard library integer types

• Float and Double

• Bool

• Date and NSDate

• NSAttributedString

• NSNumber

• NSRange

• URL and NSURL

• CGPoint, CGSize, and CGRect

• NSColor, UIColor, CGColor, and CIColor

• NSImage, UIImage, CGImage, and CIImage

• NSBezierPath and UIBezierPath

• NSView and UIView

Playground logging may also be able to support specialized descriptions of other types.

Conforming to the CustomPlaygroundDisplayConvertible Protocol

To add CustomPlaygroundDisplayConvertible conformance to your custom type, implement the playgroundDescription property. If your implementation returns an instance of one of the types above, that type’s specialized description is used. If you return any other type, a structured description is generated.

If your type has value semantics, the playgroundDescription should be unaffected by subsequent mutations, if possible.

If your type’s playgroundDescription returns an instance which itself conforms to CustomPlaygroundDisplayConvertible, then that type’s playgroundDescription will be used, and so on. To prevent infinite loops, playground logging implementations can place a reasonable limit on this kind of chaining.