C#的运算符重载是什么？如何为自定义类型定义运算符行为？

public struct Complex
{
    public double Real { get; }
    public double Imaginary { get; }

    public Complex(double real, double imaginary)
    {
        Real = real;
        Imaginary = imaginary;
    }

    // 重载 + 运算符
    public static Complex operator +(Complex a, Complex b)
    {
        return new Complex(a.Real + b.Real, a.Imaginary + b.Imaginary);
    }

    // 重载 == 运算符
    public static bool operator ==(Complex a, Complex b)
    {
        return a.Real == b.Real && a.Imaginary == b.Imaginary;
    }

    // 重载 != 运算符
    public static bool operator !=(Complex a, Complex b)
    {
        return !(a == b);
    }

    // 重写 Equals 方法以保持一致性
    public override bool Equals(object obj)
    {
        if (obj is Complex c)
            return this == c;
        return false;
    }

    // 重写 GetHashCode
    public override int GetHashCode()
    {
        return HashCode.Combine(Real, Imaginary);
    }
}