Avoiding duplication of property names

FormatOptions.swift

// For https://twitter.com/nicklockwood/status/819938181483233285

protocol Withable {
    init()
}

extension Withable {
    func with(_ body: (inout Self) -> ()) -> Self {
        var copy = self
        body(&copy)
        return copy
    }

    init(_ body: (inout Self) -> ()) {
        self.init()
        body(&self)
    }
}

public enum WrapMode { case disabled, beforeFirst }
public enum IndentMode { case indent }

public struct FormatOptions {
    public var indent = "    "
    public var linebreak = "\n"
    public var allowInlineSemicolons = true
    public var spaceAroundRangeOperators = true
    public var useVoid = true
    public var trailingCommas = true
    public var trailingClosures = false
    public var indentComments = true
    public var truncateBlankLines = true
    public var insertBlankLines = true
    public var removeBlankLines = true
    public var allmanBraces = false
    public var stripHeader = false
    public var ifdefIndent = IndentMode.indent
    public var wrapArguments = WrapMode.disabled
    public var wrapElements = WrapMode.beforeFirst
    public var uppercaseHex = true
    public var experimentalRules = false
    public var fragment = false
}

extension FormatOptions: Withable { }

let options1 = FormatOptions { $0.fragment = true; $0.wrapArguments = .beforeFirst }
let options2 = options1.with({ $0.uppercaseHex = false; $0.trailingCommas = false })