ReversibleFormatStyle - like FormatStyle but reversible, more like Formatter

reversible-formatstyle.swift

import Foundation

// like FormatStyle but reversible, more like Formatter
protocol ReversibleFormatStyle<FormatOutput>: FormatStyle {
	func format(_ value: FormatOutput) -> FormatInput
}

// Implementation

struct ReversibleNumFormatStyle: ReversibleFormatStyle {
	typealias FormatInput = Double
	typealias FormatOutput = String
	
	func format(_ value: Double) -> String {
		value.formatted()
	}

	func format(_ value: String) -> Double {
		Double(value) ?? 0
	}

}

// Usage

let input: Double = 1.0
print("input : \(input) \(type(of: input))")

let formatStyle = ReversibleNumFormatStyle()

let output = formatStyle.format(input) as String
print("output: \(output) \(type(of: output))")
let revInput = formatStyle.format(output) as Double
print("revers: \(revInput) \(type(of: revInput))")

// ----------
// input : 1.0 Double
// output: 1 String
// revers: 1.0 Double