Fortify your code with runtime checks, and examine your values' runtime representation.
Debugging and Reflection
Topics
Printing and Dumping
func print(Any, separator: String, terminator: String)Writes the textual representations of the given items into the standard output.
func print<Target>(Any, separator: String, terminator: String, to: inout Target)Writes the textual representations of the given items into the given output stream.
func debugWrites the textual representations of the given items most suitable for debugging into the standard output.
func debugWrites the textual representations of the given items most suitable for debugging into the given output stream.
func dump<T>(T, name: String?, indent: Int, maxDumps the given object’s contents using its mirror to standard output.
func dump<T, TargetDumps the given object’s contents using its mirror to the specified output stream.
Testing
func assert(() -> Bool, () -> String, file: StaticPerforms a traditional C-style assert with an optional message.
func assertionIndicates that an internal sanity check failed.
func precondition(() -> Bool, () -> String, file: StaticChecks a necessary condition for making forward progress.
func preconditionIndicates that a precondition was violated.
Exiting a Program
func fatalUnconditionally prints a given message and stops execution.
enum NeverThe return type of functions that do not return normally, that is, a type with no values.
Querying Runtime Values
struct MirrorA representation of the substructure and display style of an instance of any type.
struct ObjectA unique identifier for a class instance or metatype.
func type<T, Metatype>(of: T) -> MetatypeReturns the dynamic type of a value.
func == (AnyReturns a Boolean value indicating whether two types are identical.
func != (AnyReturns a Boolean value indicating whether two types are not identical.
Customizing Your Type's Reflection
Provide a custom reflection for your types using these protocols.
protocol CustomA type that explicitly supplies its own mirror.
protocol CustomA type that explicitly supplies its own mirror, but whose descendant classes are not represented in the mirror unless they also override custom.
protocol CustomA type that supplies a custom description for playground logging.
typealias PlaygroundThe sum of types that can be used as a Quick Look representation.
See Also
Programming Tasks
Input and Output
Print values to the console, read from and write to text streams, and use command line arguments.
Key-Path Expressions
Use key-path expressions to access properties dynamically.
Manual Memory Management
Allocate and manage memory manually.
Type Casting and Existential Types
Perform casts between types or represent values of any type.
C Interoperability
Use imported C types or call C variadic functions.
Operator Declarations
Work with prefix, postfix, and infix operators.