Is there a way to use tabs to evenly space out description strings in Swift?

Question

Overriding the description variable of a custom class:

override var description : String {
        let mirrored_object = Mirror(reflecting: self)
        let         


        

Answer 1

I wouldn't use tabs but use padding(...):

var description : String {
    let mirrored_object = Mirror(reflecting: self)
    let childrenWithLabel = mirrored_object.children.filter { $0.label != nil }
    let maxLen = childrenWithLabel.map { Int($0.label!.characters.count) }.max() ?? 0
    let lines = childrenWithLabel.map { $0.label!.padding(toLength: maxLen, withPad: " ", startingAt: 0) + " = \($0.value)" }
    return lines.joined(separator: "\n")
}

For a struct like

struct Foo: CustomStringConvertible
{
    let userID = 42
    let username = "Foo"
    let verylongpropertyname: String? = "Bar"
}

this produces

userID               = 42
username             = Foo
verylongpropertyname = Optional("Bar")

As for the "Optional" part, it's not as easy as totiG suggests because the value you get from the mirror is of type Any. See this question.

Update

I overlooked that you wanted to have a slightly different format.

var description : String {
    let mirrored_object = Mirror(reflecting: self)
    let childrenWithLabel = mirrored_object.children.filter { $0.label != nil }
    let separator = " = "
    let firstColumnWidth = (childrenWithLabel.map { Int($0.label!.characters.count) }.max() ?? 0) + separator.characters.count
    let lines = childrenWithLabel.map {
        ($0.label! + separator).padding(toLength: firstColumnWidth, withPad: " ", startingAt: 0) + "\($0.value)"
    }
}

produces

userID =               42
username =             Foo
verylongpropertyname = Optional("Bar")

Update 2

To get rid of the "Optional" thing, please see my answer here.

If you use (from said answer) unwrap() or unwrapUsingProtocol() in description like this:

var description : String {
    let mirrored_object = Mirror(reflecting: self)
    let childrenWithLabel = mirrored_object.children.filter { $0.label != nil }
    let separator = " = "
    let firstColumnWidth = (childrenWithLabel.map { Int($0.label!.characters.count) }.max() ?? 0) + separator.characters.count
    let lines = childrenWithLabel.map {
        ($0.label! + separator).padding(toLength: firstColumnWidth, withPad: " ", startingAt: 0) + "\(unwrap($0.value))"
    }
    return lines.joined(separator: "\n")
}

this will produce

userID =               42
username =             Foo
verylongpropertyname = Bar

Answer 2

Try use this method. It first calculates the max length of the property, and then uses that to pad the property names:

let maxPropertyLength: Int = mirrored_object.children.map { Int($0.label?.characters.count ?? 0) }.max() ?? 0
for attr in mirrored_object.children {
    if let propertyName = attr.label {
        str.append("\(propertyName.padding(toLength: maxPropertyLength + 2, withPad: " ", startingAt: 0)) = \(attr.value)\n")
    }
}
return str as String