Is there a way to pretty print Swift dictionaries to the console?

Question

NSDictionary *dictionary = @{@\"A\" : @\"alfa\",
                             @\"B\" : @\"bravo\",
                             @\"C\" : @\"charlie\",
                       


        

Answer 1

How about:

import Foundation

extension Dictionary {
    var myDesc: String {
        get {
            var v = ""
            for (key, value) in self {
                v += ("\(key) = \(value)\n")
            }
            return v
        }
    }
}


// Then, later, for any dictionary:
print(dictionary.myDesc)

Answer 2

I wouldn't consider a lot of the answers provided here true pretty printed JSON, as when you pass the results into a JSON validator the result is invalid (often due to the code including '=' rather than ':').

The easiest way I've found of doing this is just converting the JSON object to data using the pretty printed writing option then printing a string using the resulting data.

Here is an example:

let jsonData = try! JSONSerialization.data(withJSONObject: parameters, options: .prettyPrinted)

if let jsonString = String(data: jsonData, encoding: .utf8) {
    print(jsonString)
}

Result:

{
    "jsonData": [
        "Some String"
    ],
    "moreJSONData": "Another String",
    "evenMoreJSONData": {
        "A final String": "awd"
    }
}

EDIT: It's been pointed out that the OP did not ask for JSON, however I find that the answers that recommend just printing or dumping the data into the console provide very little formatting (if any) and are therefore not pretty printing.

I believe that despite the OP not asking for JSON, it is a viable answer as it is a much more readable format for data than the horrendous format that is spat out into the console by xcode/swift.

Answer 3

You could use dump, for example, if the goal is to inspect the dictionary. dump is part of Swift's standard library.

Usage:

let dictionary: [String : String] = ["A" : "alfa",
                                     "B" : "bravo",
                                     "C" : "charlie",
                                     "D" : "delta",
                                     "E" : "echo",
                                     "F" : "foxtrot"]

dump(dictionary)

Output:

---

dump prints the contents of an object via reflection (mirroring).

Detailed view of an array:

let names = ["Joe", "Jane", "Jim", "Joyce"]
dump(names)

Prints:

▿ 4 elements
- [0]: Joe
- [1]: Jane
- [2]: Jim
- [3]: Joyce

For a dictionary:

let attributes = ["foo": 10, "bar": 33, "baz": 42]
dump(attributes)

Prints:

▿ 3 key/value pairs
▿ [0]: (2 elements)
- .0: bar
- .1: 33
▿ [1]: (2 elements)
- .0: baz
- .1: 42
▿ [2]: (2 elements)
- .0: foo
- .1: 10

dump is declared as dump(_:name:indent:maxDepth:maxItems:).

The first parameter has no label.

There's other parameters available, like name to set a label for the object being inspected:

dump(attributes, name: "mirroring")

Prints:

▿ mirroring: 3 key/value pairs
▿ [0]: (2 elements)
- .0: bar
- .1: 33
▿ [1]: (2 elements)
- .0: baz
- .1: 42
▿ [2]: (2 elements)
- .0: foo
- .1: 10

You can also choose to print only a certain number of items with maxItems:, to parse the object up to a certain depth with maxDepth:, and to change the indentation of printed objects with indent:.

Answer 4

For Swift 3 (& building on the brilliant answer by @Jalakoo), make the following Dictionary extension:

extension Dictionary where Key: ExpressibleByStringLiteral, Value: Any {
    var prettyPrint: String {
        return String(describing: self as AnyObject)
    }
}

then print a dictionary of any hierarchy in a pretty way (better than dump()) using this:

print(dictionary!.prettyPrint)

Answer 5

Adjusted based on my other answer here.

PrettyPrint JSON solution using LLDB alias

✨No code needed ✨

• To get a nice json formatting (indentations, newlines, etc) you can define an lldb alias by running this command in your lldb terminal (source):

command regex pjson 's/(.+)/expr print(NSString(string: String(data: try! JSONSerialization.data(withJSONObject: %1, options: .prettyPrinted), encoding: .utf8)!))/'

• You probably don't want to re-define the alias everytime you open XCode, so run the following command to append the alias definition to ~/.lldbinit:

echo "command regex pjson 's/(.+)/expr print(NSString(string: String(data: try! JSONSerialization.data(withJSONObject: %1, options: .prettyPrinted), encoding: .utf8)!))/'" >> ~/.lldbinit

• This will create the pjson alias which you can use in your lldb terminal in XCode:

pjson object

---

Comparing the outputs for the following Swift object:

// Using Any? to demo optional & arbitrary Type
let dictionary: Any? = [
    "embedded": [
        "JustForTheSakeOfTheDemo": 42
    ],
    "A" : "alfa",
    "B" : "bravo",
    "C" : "charlie",
    "D" : "delta",
    "E" : "echo",
    "F" : "foxtrot"
]

✅ Output of pjson dictionary

{
  "F" : "foxtrot",
  "D" : "delta",
  "embedded" : {
    "JustForTheSakeOfTheDemo" : 42
  },
  "E" : "echo",
  "A" : "alfa",
  "C" : "charlie",
  "B" : "bravo"
}

❌ Output of p dictionary

(Any?) $R0 = 7 key/value pairs {
  [0] = {
    key = "F"
    value = "foxtrot"
  }
  [1] = {
    key = "D"
    value = "delta"
  }
  [2] = {
    key = "embedded"
    value = 1 key/value pair {
      [0] = (key = "JustForTheSakeOfTheDemo", value = 42)
    }
  }
  [3] = {
    key = "E"
    value = "echo"
  }
  [4] = {
    key = "A"
    value = "alfa"
  }
  [5] = {
    key = "C"
    value = "charlie"
  }
  [6] = {
    key = "B"
    value = "bravo"
  }
}

❌ Output of p (dictionary as! NSDictionary)

(NSDictionary) $R18 = 0x0000000281e89710 {
  ObjectiveC.NSObject = {
    base__SwiftNativeNSDictionaryBase@0 = {
      baseNSDictionary@0 = {
        NSObject = {
          isa = Swift._SwiftDeferredNSDictionary<Swift.String, Any> with unmangled suffix "$"
        }
      }
    }
  }
}

❌ Output of po dictionary

▿ Optional<Any>
  ▿ some : 7 elements
    ▿ 0 : 2 elements
      - key : "F"
      - value : "foxtrot"
    ▿ 1 : 2 elements
      - key : "D"
      - value : "delta"
    ▿ 2 : 2 elements
      - key : "embedded"
      ▿ value : 1 element
        ▿ 0 : 2 elements
          - key : "JustForTheSakeOfTheDemo"
          - value : 42
    ▿ 3 : 2 elements
      - key : "E"
      - value : "echo"
    ▿ 4 : 2 elements
      - key : "A"
      - value : "alfa"
    ▿ 5 : 2 elements
      - key : "C"
      - value : "charlie"
    ▿ 6 : 2 elements
      - key : "B"
      - value : "bravo"

❌ Output of po print(dictionary)

Optional(["F": "foxtrot", "D": "delta", "embedded": ["JustForTheSakeOfTheDemo": 42], "E": "echo", "A": "alfa", "C": "charlie", "B": "bravo"])

Answer 6

Pretty print from Data object:

let jsonObj = try JSONSerialization.jsonObject(with: data, options: [])
            let jsonData = try JSONSerialization.data(withJSONObject: jsonObj, options: [.prettyPrinted])
            print(String(data: jsonData, encoding: .utf8)!)