How to pretty print a nested composite object structure conforming to CustomDebugStringConvertible

Question

I am trying to pretty-print (with indentation for child objects) a composite object structure where the parent and each of the child objects confirm to the CustomDebugStringConvertible protocol.

My code so far is: import Foundation

class StringUtils {
    static func appendIfValuePresent(key: String, value: AnyHashable?, toArray array: inout [String], separator: String = ": ") {
        if let value = value {
            array.append("\(key)\(separator)\(value)")
        }
    }
}

class Address: CustomDebugStringConvertible {
    var city: String? = "B'lore"
    var country: String? = "India"
    var pincode: String? = nil

    var debugDescription: String {
        var components = [String]()
        StringUtils.appendIfValuePresent(key: "city", value: city, toArray: &components)
        StringUtils.appendIfValuePresent(key: "country", value: country, toArray: &components)
        StringUtils.appendIfValuePresent(key: "pincode", value: pincode, toArray: &components)
        let debugStr = components.joined(separator: "\n")
        return debugStr
    }
}

class Contact: CustomDebugStringConvertible {
    var phNum: String? = "111-222-33"
    var email: String? = "[email protected]"
    var address: Address? = Address()

    var debugDescription: String {
        var components = [String]()
        StringUtils.appendIfValuePresent(key: "phNum", value: phNum, toArray: &components)
        StringUtils.appendIfValuePresent(key: "email", value: email, toArray: &components)
        StringUtils.appendIfValuePresent(key: "address", value: address?.debugDescription, toArray: &components, separator: ":\n")
        let debugStr = components.joined(separator: "\n")
        return debugStr
    }
}

class Student: CustomDebugStringConvertible {
    var name = "ron"
    var contact: Contact? = Contact()
    var debugDescription: String {
        var components = [String]()
        StringUtils.appendIfValuePresent(key: "name", value: name, toArray: &components)
        StringUtils.appendIfValuePresent(key: "contact", value: contact?.debugDescription, toArray: &components, separator: ":\n")
        let debugStr = components.joined(separator: "\n")
        return debugStr
    }
}

let student = Student()

print(student)

The output of the above code snippet is:

// Actual output
/*
 name: ron
 contact:
 phNum: 111-222-33
 email: [email protected]
 address:
 city: B'lore
 country: India
*/

However, I would like to print like this:

// Expected output
/*
 name: ron
 contact:
    phNum: 111-222-33
    email: [email protected]
    address:
        city: B'lore
        country: India
*/

What is the best way to achieve this, retaining the generic structure of the code?

Answer 1

I could devise a solution to my problem and posted a solution here: https://gist.github.com/raunakp/16155d19d005939f1297b7c6cb6f890c

import Foundation

class StringUtils {
    static func appendIfValuePresent(key: String, value: AnyHashable?, toArray array: inout [String], separator: String = ": ") {
        if let value = value {
            array.append("\(key)\(separator)\(value)")
        }
    }
}

struct PrettyPrintableComponent {
    var indentationLevel = 0
    var indentationSeparator = "\t"
    var lineSeparator = "\n"
}

protocol HasPrettyPrintableComponent {
    var prettyPrintableComponent: PrettyPrintableComponent { get set }
}

protocol PrettyDebugPrintable: HasPrettyPrintableComponent, CustomDebugStringConvertible { }

extension PrettyDebugPrintable {
    var indentationLevel: Int {
        get { return prettyPrintableComponent.indentationLevel }
        set { prettyPrintableComponent.indentationLevel = newValue }
    }
    var indentationSeparator: String {
        get { return prettyPrintableComponent.indentationSeparator }
        set { prettyPrintableComponent.indentationSeparator = newValue }
    }
    var lineSeparator: String {
        get { return prettyPrintableComponent.lineSeparator }
        set { prettyPrintableComponent.lineSeparator = newValue }
    }
}

class Address: PrettyDebugPrintable {
    var city: String? = "B'lore"
    var country: String? = "India"
    var pincode: String? = nil

    var prettyPrintableComponent = PrettyPrintableComponent()

    var debugDescription: String {
        var components = [String]()
        StringUtils.appendIfValuePresent(key: "city", value: city, toArray: &components)
        StringUtils.appendIfValuePresent(key: "country", value: country, toArray: &components)
        StringUtils.appendIfValuePresent(key: "pincode", value: pincode, toArray: &components)
        let indentationSeparator = String.init(repeating: prettyPrintableComponent.indentationSeparator, count: prettyPrintableComponent.indentationLevel)
        let debugStr = indentationSeparator + components.joined(separator: prettyPrintableComponent.lineSeparator + indentationSeparator)
        return debugStr
    }
}

class Contact: PrettyDebugPrintable {
    var phNum: String? = "111-222-33"
    var email: String? = "[email protected]"
    var address: Address? = Address()

    var prettyPrintableComponent = PrettyPrintableComponent()

    var debugDescription: String {
        var components = [String]()
        StringUtils.appendIfValuePresent(key: "phNum", value: phNum, toArray: &components)
        StringUtils.appendIfValuePresent(key: "email", value: email, toArray: &components)
        address?.prettyPrintableComponent.indentationLevel = self.prettyPrintableComponent.indentationLevel + 1
        StringUtils.appendIfValuePresent(key: "address", value: address?.debugDescription, toArray: &components, separator: ":\n")
        let indentationSeparator = String.init(repeating: prettyPrintableComponent.indentationSeparator, count: prettyPrintableComponent.indentationLevel)
        let debugStr = indentationSeparator + components.joined(separator: prettyPrintableComponent.lineSeparator + indentationSeparator)
        return debugStr
    }
}

class Student: PrettyDebugPrintable {
    var name = "ron"
    var contact: Contact? = Contact()

    var prettyPrintableComponent = PrettyPrintableComponent()

    var debugDescription: String {
        var components = [String]()
        StringUtils.appendIfValuePresent(key: "name", value: name, toArray: &components)
        contact?.prettyPrintableComponent.indentationLevel = self.prettyPrintableComponent.indentationLevel + 1
        StringUtils.appendIfValuePresent(key: "contact", value: contact?.debugDescription, toArray: &components, separator: ":\n")
        let indentationSeparator = String.init(repeating: prettyPrintableComponent.indentationSeparator, count: prettyPrintableComponent.indentationLevel)
        let debugStr = indentationSeparator + components.joined(separator: prettyPrintableComponent.lineSeparator + indentationSeparator)
        return debugStr
    }
}

let student = Student()

print(student)

// output
/*
name: ron
contact:
    phNum: 111-222-33
    email: [email protected]
    address:
        city: B'lore
        country: India
*/