Measurement.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

import CoreFoundation

/// A `Measurement` is a model type that holds a `Double` value associated with a `Unit`.
///
/// Measurements support a large set of operators, including `+`, `-`, `*`, `/`, and a full set of comparison operators.
public struct Measurement<UnitType : Unit> : ReferenceConvertible, Comparable, Equatable, CustomStringConvertible {
    public typealias ReferenceType = NSMeasurement
    
    /// The unit component of the `Measurement`.
    public let unit: UnitType
    
    /// The value component of the `Measurement`.
    public var value: Double
    
    /// Create a `Measurement` given a specified value and unit.
    public init(value: Double, unit: UnitType) {
        self.value = value
        self.unit = unit
    }
    
    public var hashValue: Int {
        return Int(bitPattern: _CFHashDouble(value))
    }
    
    public var description: String {
        return "\(value) \(unit.symbol)"
    }
    
    public var debugDescription: String {
        return "\(value) \(unit.symbol)"
    }
}

/// When a `Measurement` contains a `Dimension` unit, it gains the ability to convert between the kinds of units in that dimension.
extension Measurement where UnitType : Dimension {
    /// Returns a new measurement created by converting to the specified unit.
    ///
    /// - parameter otherUnit: A unit of the same `Dimension`.
    /// - returns: A converted measurement.
    public func converted(to otherUnit: UnitType) -> Measurement<UnitType> {
        if unit.isEqual(otherUnit) {
            return Measurement(value: value, unit: otherUnit)
        } else {
            let valueInTermsOfBase = unit.converter.baseUnitValue(fromValue: value)
            if otherUnit.isEqual(type(of: unit).baseUnit()) {
                return Measurement(value: valueInTermsOfBase, unit: otherUnit)
            } else {
                let otherValueFromTermsOfBase = otherUnit.converter.value(fromBaseUnitValue: valueInTermsOfBase)
                return Measurement(value: otherValueFromTermsOfBase, unit: otherUnit)
            }
        }
    }
    
    /// Converts the measurement to the specified unit.
    ///
    /// - parameter otherUnit: A unit of the same `Dimension`.
    public mutating func convert(to otherUnit: UnitType) {
        self = converted(to: otherUnit)
    }
    
}

/// Add two measurements of the same Unit.
/// - precondition: The `unit` of `lhs` and `rhs` must be `isEqual`.
/// - returns: A measurement of value `lhs.value + rhs.value` and unit `lhs.unit`.
public func +<UnitType>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Measurement<UnitType> {
    if lhs.unit.isEqual(rhs.unit) {
        return Measurement(value: lhs.value + rhs.value, unit: lhs.unit)
    } else {
        fatalError("Attempt to add measurements with non-equal units")
    }
}

/// Add two measurements of the same Dimension.
///
/// If the `unit` of the `lhs` and `rhs` are `isEqual`, then this returns the result of adding the `value` of each `Measurement`. If they are not equal, then this will convert both to the base unit of the `Dimension` and return the result as a `Measurement` of that base unit.
/// - returns: The result of adding the two measurements.
public func +<UnitType : Dimension>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Measurement<UnitType> {
    if lhs.unit.isEqual(rhs.unit) {
        return Measurement(value: lhs.value + rhs.value, unit: lhs.unit)
    } else {
        let lhsValueInTermsOfBase = lhs.unit.converter.baseUnitValue(fromValue: lhs.value)
        let rhsValueInTermsOfBase = rhs.unit.converter.baseUnitValue(fromValue: rhs.value)
        return Measurement(value: lhsValueInTermsOfBase + rhsValueInTermsOfBase, unit: type(of: lhs.unit).baseUnit())
    }
}

/// Subtract two measurements of the same Unit.
/// - precondition: The `unit` of `lhs` and `rhs` must be `isEqual`.
/// - returns: A measurement of value `lhs.value - rhs.value` and unit `lhs.unit`.
public func -<UnitType>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Measurement<UnitType> {
    if lhs.unit.isEqual(rhs.unit) {
        return Measurement(value: lhs.value - rhs.value, unit: lhs.unit)
    } else {
        fatalError("Attempt to subtract measurements with non-equal units")
    }
}

/// Subtract two measurements of the same Dimension.
///
/// If the `unit` of the `lhs` and `rhs` are `==`, then this returns the result of subtracting the `value` of each `Measurement`. If they are not equal, then this will convert both to the base unit of the `Dimension` and return the result as a `Measurement` of that base unit.
/// - returns: The result of adding the two measurements.
public func -<UnitType : Dimension>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Measurement<UnitType> {
    if lhs.unit == rhs.unit {
        return Measurement(value: lhs.value - rhs.value, unit: lhs.unit)
    } else {
        let lhsValueInTermsOfBase = lhs.unit.converter.baseUnitValue(fromValue: lhs.value)
        let rhsValueInTermsOfBase = rhs.unit.converter.baseUnitValue(fromValue: rhs.value)
        return Measurement(value: lhsValueInTermsOfBase - rhsValueInTermsOfBase, unit: type(of: lhs.unit).baseUnit())
    }
}

/// Multiply a measurement by a scalar value.
/// - returns: A measurement of value `lhs.value * rhs` with the same unit as `lhs`.
public func *<UnitType>(lhs: Measurement<UnitType>, rhs: Double) -> Measurement<UnitType> {
    return Measurement(value: lhs.value * rhs, unit: lhs.unit)
}

/// Multiply a scalar value by a measurement.
/// - returns: A measurement of value `lhs * rhs.value` with the same unit as `rhs`.
public func *<UnitType>(lhs: Double, rhs: Measurement<UnitType>) -> Measurement<UnitType> {
    return Measurement(value: lhs * rhs.value, unit: rhs.unit)
}

/// Divide a measurement by a scalar value.
/// - returns: A measurement of value `lhs.value / rhs` with the same unit as `lhs`.
public func /<UnitType>(lhs: Measurement<UnitType>, rhs: Double) -> Measurement<UnitType> {
    return Measurement(value: lhs.value / rhs, unit: lhs.unit)
}

/// Divide a scalar value by a measurement.
/// - returns: A measurement of value `lhs / rhs.value` with the same unit as `rhs`.
public func /<UnitType>(lhs: Double, rhs: Measurement<UnitType>) -> Measurement<UnitType> {
    return Measurement(value: lhs / rhs.value, unit: rhs.unit)
}

/// Compare two measurements of the same `Unit`.
/// - returns: `true` if `lhs.value == rhs.value && lhs.unit == rhs.unit`.
public func ==<UnitType>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Bool {
    return lhs.value == rhs.value && lhs.unit == rhs.unit
}

/// Compare two measurements of the same `Dimension`.
///
/// If `lhs.unit == rhs.unit`, returns `lhs.value == rhs.value`. Otherwise, converts `rhs` to the same unit as `lhs` and then compares the resulting values.
/// - returns: `true` if the measurements are equal.
public func ==<UnitType : Dimension>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Bool {
    if lhs.unit == rhs.unit {
        return lhs.value == rhs.value
    } else {
        let rhsInLhs = rhs.converted(to: lhs.unit)
        return lhs.value == rhsInLhs.value
    }
}

/// Compare two measurements of the same `Unit`.
/// - note: This function does not check `==` for the `unit` property of `lhs` and `rhs`.
/// - returns: `lhs.value < rhs.value`
public func <<UnitType>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Bool {
    return lhs.value < rhs.value
}

/// Compare two measurements of the same `Dimension`.
///
/// If `lhs.unit == rhs.unit`, returns `lhs.value < rhs.value`. Otherwise, converts `rhs` to the same unit as `lhs` and then compares the resulting values.
/// - returns: `true` if `lhs` is less than `rhs`.
public func <<UnitType : Dimension>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Bool {
    if lhs.unit == rhs.unit {
        return lhs.value < rhs.value
    } else {
        let rhsInLhs = rhs.converted(to: lhs.unit)
        return lhs.value < rhsInLhs.value
    }
}

/// Compare two measurements of the same `Unit`.
/// - note: This function does not check `==` for the `unit` property of `lhs` and `rhs`.
/// - returns: `lhs.value > rhs.value`
public func ><UnitType>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Bool {
    return lhs.value > rhs.value
}

/// Compare two measurements of the same `Dimension`.
///
/// If `lhs.unit == rhs.unit`, returns `lhs.value > rhs.value`. Otherwise, converts `rhs` to the same unit as `lhs` and then compares the resulting values.
/// - returns: `true` if `lhs` is greater than `rhs`.
public func ><UnitType : Dimension>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Bool {
    if lhs.unit == rhs.unit {
        return lhs.value > rhs.value
    } else {
        let rhsInLhs = rhs.converted(to: lhs.unit)
        return lhs.value > rhsInLhs.value
    }
}

/// Compare two measurements of the same `Unit`.
/// - note: This function does not check `==` for the `unit` property of `lhs` and `rhs`.
/// - returns: `lhs.value <= rhs.value`
public func <=<UnitType>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Bool {
    return lhs.value <= rhs.value
}

/// Compare two measurements of the same `Dimension`.
///
/// If `lhs.unit == rhs.unit`, returns `lhs.value < rhs.value`. Otherwise, converts `rhs` to the same unit as `lhs` and then compares the resulting values.
/// - returns: `true` if `lhs` is less than or equal to `rhs`.
public func <=<UnitType : Dimension>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Bool {
    if lhs.unit == rhs.unit {
        return lhs.value <= rhs.value
    } else {
        let rhsInLhs = rhs.converted(to: lhs.unit)
        return lhs.value <= rhsInLhs.value
    }
}

/// Compare two measurements of the same `Unit`.
/// - note: This function does not check `==` for the `unit` property of `lhs` and `rhs`.
/// - returns: `lhs.value >= rhs.value`
public func >=<UnitType>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Bool {
    return lhs.value >= rhs.value
}

/// Compare two measurements of the same `Dimension`.
///
/// If `lhs.unit == rhs.unit`, returns `lhs.value >= rhs.value`. Otherwise, converts `rhs` to the same unit as `lhs` and then compares the resulting values.
/// - returns: `true` if `lhs` is greater or equal to `rhs`.
public func >=<UnitType : Dimension>(lhs: Measurement<UnitType>, rhs: Measurement<UnitType>) -> Bool {
    if lhs.unit == rhs.unit {
        return lhs.value >= rhs.value
    } else {
        let rhsInLhs = rhs.converted(to: lhs.unit)
        return lhs.value >= rhsInLhs.value
    }
}

// Implementation note: similar to NSArray, NSDictionary, etc., NSMeasurement's import as an ObjC generic type is suppressed by the importer. Eventually we will need a more general purpose mechanism to correctly import generic types.

extension Measurement : _ObjectTypeBridgeable {
    public static func _isBridgedToObjectiveC() -> Bool {
        return true
    }
    
    @_semantics("convertToObjectiveC")
    public func _bridgeToObjectiveC() -> NSMeasurement {
        return NSMeasurement(doubleValue: value, unit: unit)
    }
    
    public static func _forceBridgeFromObjectiveC(_ source: NSMeasurement, result: inout Measurement?) {
        result = Measurement(value: source.doubleValue, unit: source.unit as! UnitType)
    }
    
    public static func _conditionallyBridgeFromObjectiveC(_ source: NSMeasurement, result: inout Measurement?) -> Bool {
        if let u = source.unit as? UnitType {
            result = Measurement(value: source.doubleValue, unit: u)
            return true
        } else {
            return false
        }
    }
    
    public static func _unconditionallyBridgeFromObjectiveC(_ source: NSMeasurement?) -> Measurement {
        let u = source!.unit as! UnitType
        return Measurement(value: source!.doubleValue, unit: u)
    }
}