convertible.swift

/*

erica sadun ericasadun.com
Math Types
Swift2

*/

import Foundation
import QuartzCore

// MARK: Conversion

//: Numbers that can be represented as Double instances
public protocol DoubleRepresentable {
    var doubleValue: Double {get}
}

//: Numbers that convert to other types
public protocol ConvertibleNumberType: DoubleRepresentable {
    var floatValue: Float { get }
    var intValue: Int { get }
    var CGFloatValue: CGFloat { get }
}

// Default conversion implementation
public extension ConvertibleNumberType {
    public var floatValue: Float {get {return Float(doubleValue)}}
    public var intValue: Int {get {return lrint(doubleValue)}}
    public var CGFloatValue: CGFloat {get {return CGFloat(doubleValue)}}
}

extension Double: ConvertibleNumberType {public var doubleValue: Double {return self}}
extension Int: ConvertibleNumberType {public var doubleValue: Double {return Double(self)}}
extension CGFloat: ConvertibleNumberType {public var doubleValue: Double {return Double(self)}}
extension Float: ConvertibleNumberType {public var doubleValue: Double {return Double(self)}}

public extension ConvertibleNumberType {
    public func toPrecision(digits: Int) -> String {
        if digits == 0 {return "\(lrint(self.doubleValue))"}
        let factor = pow(10.0, Double(digits))
        let trunc = round(doubleValue * factor) / factor
        var result = "\(trunc)"
        while result.rangeOfString(".")?.startIndex.distanceTo(result.endIndex) < (digits + 1) {
            result += "0"
        }
        return result
    }
}