Swiftpack.co - Package - Sajjon/DelTal

DelTal

Conform to Swift protocol UnsignedInteger by proxy with the option of adding bounds using a typealias.

This way you can follow Object Callestnics's (making you a better programmer) third rule 'Wrap All Primitives And Strings' for your number types in the most convenient way. While still having the power of Swift's UnsignedInteger (and thus BinaryInteger) protocol, making your code both type safe, easy to read and convenient to use.

Example

Imagine you want to define a UInt256 and a UInt512 and a UInt4096 or what ever. Using excellent attaswift/BigInt we have a BigInt type. Using that and this Swift package, we can easily create those types and let them automagically conform to UnsignedInteger protocol.

Simplest example is using AnyUnsignedInteger, like this:

typealias BigNumber = AnyUnsignedInteger<BigUInt>

Where AnyUnsignedInteger is just a typealias itself:

typealias AnyUnsignedInteger<Value> = BUNCInt<
    NoBound<Value>,
    AnyUnsignedIntegerName,
    InfiniteInteger
> where Value: BinaryInteger, Value.Magnitude == Value

struct InfiniteInteger: IntegerCategory {
    public static let nameOfCategory = "Infinite Integer"
}

struct AnyUnsignedIntegerName: IntegerName {
    public static let nameOfInteger = "AnyUnsignedInteger"
}

Where BUNCInt is this generic struct:

struct BUNCInt<MagnitudeChecker, Name, Category>`

BUNCInt is short Bound Unsigned Named Categorized Integer for which conforms to the protocol UnsignedIntegerSynthesizedByProxy, which provides the default implementation of the UnsignedInteger methods/properites/inits.

But in this example it is not at all clear why we would want to use AnyUnsignedInteger<BigUInt> instead of BigUInt right away. So let's look at some more examples.

UInt256

And then:

typealias UInt256 = BUNCInt<UInt256Bound, UInt256Name, NoCategory>

The cool part is that our UInt256 now conforms to UnsignedInteger itself. So we can do arithmetic with the type.

UInt256Bound

import BigInt /* attaswift/BigInt */

struct UInt256Bound: Bound {}
extension UInt256Bound{
    typealias Value = BigUInt
    static var maxValue: Value { BigUInt(2).power(256) - 1 }
    static var minValue: Value { BigUInt.zero }
}

Positive256

In math, a positive number cannot be zero. Let's say we want to have a UInt256 that never can be zero, then let's create it using the one line typealias:

typealias Positive256 = BUNCInt<Positive256Bound, Positive256Name, NoCategory>

Where Positive256Bound is similar to UInt256Bound, but does not allow for zeros:

import BigInt /* attaswift/BigInt */

struct Positive256Bound: Bound {}
extension Positive256Bound{
    typealias Value = BigUInt
    static var maxValue: Value { UInt256Bound.maxValue }
    static var minValue: Value { 1 }
}

Name & Category

Let's say we want a Kelvin temperature integer (we only deal with integers in this Swift Package). Kelvin it can go from 0 to infinity (that's pretty hot πŸ”₯), thus it is an onbound.

But let's say we want to add some static preset values of Kelvin. If BUNCInt did not take a Name and Category as a generic, we would not have been able to only add static preset values to only the type Kelvin. But since we have generic Name and Category we can do exactly that.

public typealias Kelvin = BUNCInt<NoBound<BigUInt>, KelvinName, Temperatur>

public struct KelvinName: IntegerName {
    public static let nameOfInteger = "Kelvin"
}

public struct Temperatur: IntegerCategory {
    public static let nameOfCategory = "Temperature"
}

public extension Kelvin {
    enum Water {}
}

/* Verbose (needed) syntax for: `extension Kelvin.Water` */
public extension BUNCInt.Water where Name == KelvinName, Category == Temperatur {
    static var meltsAt: Kelvin { .init(magnitude: 273) }
    static var boilsAt: Kelvin { meltsAt + 100 }
}

Now we can use the Kelvin type like this:

func testMeltTemperatur() {
    XCTAssertEqual(Kelvin.Water.meltsAt, 273)
    XCTAssertEqual(
        Kelvin.Water.boilsAt - Kelvin.Water.meltsAt, 
        100
    )
}

Another advantage of the generic Name and Category of BUNCInt is that we get context to our values, which we are using conforming to CustomStringConvertible and CustomDebugStringConvertible, resulting in this.

func testKelvinDescription() {
    XCTAssertEqual(
        Kelvin.Water.boilsAt.description, 
        "373 Kelvin"
    )

    XCTAssertEqual(
        Kelvin.Water.boilsAt.debugDescription,
        "373 Kelvin (Temperature)"
    )
}

Installation

Swift Package Manager

dependencies: [
    .package(url: "https://github.com/Sajjon/DelTal.git", from: "0.0.1")
]

Etymology πŸ‡ΈπŸ‡ͺ

"DelTal" is a play with Swedish words. The English word "Integer" is "Heltal" in Swedish. Replacing Hel with Del, where "Del" is short for "Delegerat", meaning "Delegated" in English.

In other words, "a delegated integer", but as a Swedish pun.

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