c#编写一个表示向量(Vector)的类 ·向量的维度(Dimension)一旦确定，不可更改 。向量的长度（模,Length 提供索引器 。向量的加减法，支持与数字相加减 ·向量的点乘

在 C# 中，你可以创建一个名为 `Vector` 的类来表示二维或三维向量，确保它的属性和方法满足你所描述的要求。以下是示例代码：

public class Vector<T>
{
    private readonly int dimension;
    private T[] components;

    // 构造函数，限制维度不可更改
    public Vector(int dimension)
    {
        if (dimension <= 0)
            throw new ArgumentException("Dimension must be a positive integer.");
        
        this.dimension = dimension;
        components = new T[dimension];
    }

    // 索引器访问和修改元素
    public T this[int index]
    {
        get => components[index];
        set
        {
            if (index < 0 || index >= dimension)
                throw new IndexOutOfRangeException();
            
            components[index] = value;
        }
    }

    // 计算长度(模)
    public double Length()
    {
        double sum = 0.0;
        for (int i = 0; i < dimension; i++)
            sum += components[i].MultiplyBy(components[i]); // 假设有一个 MultiplyBy 方法用于计算平方

        return Math.Sqrt(sum);
    }

    // 加法运算符
    public Vector<T> operator +(Vector<T> other)
    {
        if (dimension != other.dimension)
            throw new ArgumentException("Vectors must have the same dimension to perform addition.");

        Vector<T> result = new Vector<T>(dimension);
        for (int i = 0; i < dimension; i++)
            result.components[i] = components[i] + other.components[i];

        return result;
    }

    // 减法运算符
    public Vector<T> operator -(Vector<T> other)
    {
        return this + (-other);
    }

    // 与数字相加减
    public Vector<T> AddOrSubtract(T scalar)
    {
        Vector<T> vectorWithScalar = new Vector<T>(dimension);
        for (int i = 0; i < dimension; i++)
            vectorWithScalar.components[i] = components[i] + scalar;

        return vectorWithScalar;
    }

    // 点乘运算
    public T DotProduct(Vector<T> other)
    {
        if (dimension != other.dimension)
            throw new ArgumentException("Vectors must have the same dimension for dot product.");

        T result = default(T);
        for (int i = 0; i < dimension; i++)
            result += components[i] * other.components[i]; // 假设MultiplyBy方法返回的是已乘积

        return result;
    }

    // 其他方法...
}

// 假设存在MultiplyBy方法来处理不同类型的数据
public static T MultiplyBy(this T num, T other)
{
    // 根据T的类型实现乘法操作
}