在 C# 中使用泛型创建数学库 [英] Creating a Math library using Generics in C#

问题描述

是否有任何可行的方法可以使用泛型来创建不依赖于选择用于存储数据的基本类型的数学库?

Is there any feasible way of using generics to create a Math library that does not depend on the base type chosen to store data?

换句话说，假设我想编写一个 Fraction 类.分数可以用两个整数或两个双精度数或诸如此类的表示.重要的是基本的四个算术运算定义明确.所以，我希望能够编写 Fraction;frac = new Fraction(1,2) 和/或 Fractionfrac = new Fraction(0.1, 1.0).

In other words, let's assume I want to write a Fraction class. The fraction can be represented by two ints or two doubles or whatnot. The important thing is that the basic four arithmetic operations are well defined. So, I would like to be able to write Fraction<int> frac = new Fraction<int>(1,2) and/or Fraction<double> frac = new Fraction<double>(0.1, 1.0).

遗憾的是没有代表四种基本操作(+、-、*、/)的接口.有没有人找到可行的、可行的方法来实现这一点?

Unfortunately there is no interface representing the four basic operations (+,-,*,/). Has anybody found a workable, feasible way of implementing this?

推荐答案

这里有一个比较简单的抽象操作符的方法.

Here is a way to abstract out the operators that is relatively painless.

    abstract class MathProvider<T>
    {
        public abstract T Divide(T a, T b);
        public abstract T Multiply(T a, T b);
        public abstract T Add(T a, T b);
        public abstract T Negate(T a);
        public virtual T Subtract(T a, T b)
        {
            return Add(a, Negate(b));
        }
    }

    class DoubleMathProvider : MathProvider<double>
    {
        public override double Divide(double a, double b)
        {
            return a / b;
        }

        public override double Multiply(double a, double b)
        {
            return a * b;
        }

        public override double Add(double a, double b)
        {
            return a + b;
        }

        public override double Negate(double a)
        {
            return -a;
        }
    }

    class IntMathProvider : MathProvider<int>
    {
        public override int Divide(int a, int b)
        {
            return a / b;
        }

        public override int Multiply(int a, int b)
        {
            return a * b;
        }

        public override int Add(int a, int b)
        {
            return a + b;
        }

        public override int Negate(int a)
        {
            return -a;
        }
    }

    class Fraction<T>
    {
        static MathProvider<T> _math;
        // Notice this is a type constructor.  It gets run the first time a
        // variable of a specific type is declared for use.
        // Having _math static reduces overhead.
        static Fraction()
        {
            // This part of the code might be cleaner by once
            // using reflection and finding all the implementors of
            // MathProvider and assigning the instance by the one that
            // matches T.
            if (typeof(T) == typeof(double))
                _math = new DoubleMathProvider() as MathProvider<T>;
            else if (typeof(T) == typeof(int))
                _math = new IntMathProvider() as MathProvider<T>;
            // ... assign other options here.

            if (_math == null)
                throw new InvalidOperationException(
                    "Type " + typeof(T).ToString() + " is not supported by Fraction.");
        }

        // Immutable impementations are better.
        public T Numerator { get; private set; }
        public T Denominator { get; private set; }

        public Fraction(T numerator, T denominator)
        {
            // We would want this to be reduced to simpilest terms.
            // For that we would need GCD, abs, and remainder operations
            // defined for each math provider.
            Numerator = numerator;
            Denominator = denominator;
        }

        public static Fraction<T> operator +(Fraction<T> a, Fraction<T> b)
        {
            return new Fraction<T>(
                _math.Add(
                  _math.Multiply(a.Numerator, b.Denominator),
                  _math.Multiply(b.Numerator, a.Denominator)),
                _math.Multiply(a.Denominator, b.Denominator));
        }

        public static Fraction<T> operator -(Fraction<T> a, Fraction<T> b)
        {
            return new Fraction<T>(
                _math.Subtract(
                  _math.Multiply(a.Numerator, b.Denominator),
                  _math.Multiply(b.Numerator, a.Denominator)),
                _math.Multiply(a.Denominator, b.Denominator));
        }

        public static Fraction<T> operator /(Fraction<T> a, Fraction<T> b)
        {
            return new Fraction<T>(
                _math.Multiply(a.Numerator, b.Denominator),
                _math.Multiply(a.Denominator, b.Numerator));
        }

        // ... other operators would follow.
    }

如果您未能实现您使用的类型，您将在运行时而不是在编译时遇到故障(这很糟糕).MathProvider 实现的定义总是相同的(也很糟糕).我建议您避免在 C# 中执行此操作，并使用 F# 或其他更适合此抽象级别的语言.

If you fail to implement a type that you use, you will get a failure at runtime instead of at compile time (that is bad). The definition of the MathProvider<T> implementations is always going to be the same (also bad). I would suggest that you just avoid doing this in C# and use F# or some other language better suited to this level of abstraction.

修正了Fraction的加减定义.另一个有趣且简单的事情是实现一个 MathProvider，它在抽象语法树上运行.这个想法立即指向做诸如自动区分之类的事情:http://conal.net/papers/beautiful-differentiation/

Fixed definitions of add and subtract for Fraction<T>. Another interesting and simple thing to do is implement a MathProvider that operates on an abstract syntax tree. This idea immediately points to doing things like automatic differentiation: http://conal.net/papers/beautiful-differentiation/

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