A type with a customized textual representation suitable for debugging purposes.


protocol CustomDebugStringConvertible


Swift provides a default debugging textual representation for any type. That default representation is used by the String(reflecting:) initializer and the debugPrint(_:) function for types that don’t provide their own. To customize that representation, make your type conform to the CustomDebugStringConvertible protocol.

Because the String(reflecting:) initializer works for instances of any type, returning an instance’s debugDescription if the value passed conforms to CustomDebugStringConvertible, accessing a type’s debugDescription property directly or using CustomDebugStringConvertible as a generic constraint is discouraged.

Conforming to the CustomDebugStringConvertible Protocol

Add CustomDebugStringConvertible conformance to your custom types by defining a debugDescription property.

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

struct Point {
    let x: Int, y: Int

let p = Point(x: 21, y: 30)
print(String(reflecting: p))
// Prints "p: Point = {
//           x = 21
//           y = 30
//         }"

After adding CustomDebugStringConvertible conformance by implementing the debugDescription property, Point provides its own custom debugging representation.

extension Point: CustomDebugStringConvertible {
    var debugDescription: String {
        return "Point(x: \(x), y: \(y))"

print(String(reflecting: p))
// Prints "Point(x: 21, y: 30)"


Instance Properties

var debugDescription: String

A textual representation of this instance, suitable for debugging.

Required. Default implementation provided.


Conforming Types

See Also

String Representation

protocol CustomStringConvertible

A type with a customized textual representation.

protocol LosslessStringConvertible

A type that can be represented as a string in a lossless, unambiguous way.