swift - 有没有办法在 Swift 中使用制表符均匀分隔描述字符串？

Question

覆盖自定义类的描述变量:

override var description : String {
        let mirrored_object = Mirror(reflecting: self)
        let str:NSMutableString = NSMutableString()
        for (index, attr) in mirrored_object.children.enumerated() {
            if let property_name = attr.label as String! {
                //str.append(" Attr \(index): \(property_name) = \(attr.value)\n")
                str.append("\t\(property_name) = \t\t\(attr.value)\n")
            }
        }
        return str as String
    }

产生如下所示的输出:

userID =        Optional(0)
username =          Optional("testuser")
email =         Optional("test@gmail.com")

有没有办法在输出中设置制表符，使属性值像这样很好地排列？

userID =        Optional(0)
username =      Optional("testuser")
email =         Optional("test@gmail.com")

还有，有没有办法去掉或缩短“可选”部分，只显示值？

Answer 1

我不会使用制表符，而是使用 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")
}

对于像这样的结构

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

这产生

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

至于“可选”部分，它并不像 totiG 所建议的那样简单，因为您从镜像中获取的值是 Any 类型。参见 this question .

更新

我忽略了您想要稍微不同的格式。

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)"
    }
}

产生

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

更新 2

要摆脱“可选”的东西，请参阅 my answer here .

如果您在 description 中使用(来自上述答案)unwrap() 或 unwrapUsingProtocol()，如下所示:

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")
}

这会产生

userID =               42
username =             Foo
verylongpropertyname = Bar