{C#}流畅方法.泛型递归

背景

• 结合泛型和递归，也能实现流畅方法，但比较烧脑
• 实现
  • Gx<T>继承Gy<T>或抽象类A(即递归)，引入Gy<T>或A的内容
  • Gn(=Gx|Gy)输入类型和方法输出类型均为T(=EmployeeDirector)，保持一致
  • Gn的方法输出类型是其子类，符合返回容器的原则
  • EmployeeDirector中的方法返回自身，符合返回容器的原则
  • 可通过EmployeeDirector类理解以上含义

示例

using static System.Console;

namespace FluentRecursiveGeneric
{
    public class Employee
    {
        public string Name { get; set; }
        public string Position { get; set; }
        public double Salary { get; set; }

        public override string ToString()
            => $"Name: {Name}, Position: {Position}, Salary: {Salary}";
    }

    public abstract class EmployeeBuilder
    {
        protected Employee employee = new Employee();

        public EmployeeBuilder() { }

        public Employee Build() => employee;
    }

    public class EmployeeNameBuilder<T> : EmployeeBuilder
        where T : EmployeeNameBuilder<T>
    {
        public T SetName(string name)
        {
            employee.Name = name;
            return (T)this; // T为当前类的子类，才能转换
        }
    }

    public class EmployeePositionBuilder<T> : EmployeeNameBuilder<T>
        where T : EmployeePositionBuilder<T>
    {
        public T SetPosition(string position)
        {
            employee.Position = position;
            return (T)this;
        }
    }

    public class EmployeeSalaryBuilder<T> : EmployeePositionBuilder<T>
        where T : EmployeeSalaryBuilder<T>
    {
        public T At(double salary)
        {
            employee.Salary = salary;
            return (T)this;
        }
    }

    // 继承薪资类取得At()方法
    // 嵌套类中均返回类型T = EmployeeDirector
    public class EmployeeDirector : EmployeeSalaryBuilder<EmployeeDirector>
    {
        // 返回容器类
        public static EmployeeDirector NewEmployee => new EmployeeDirector();
    }

    class Program
    {
        static void Main(string[] args)
        {
            var employee = EmployeeDirector.NewEmployee
                .SetName("Zhang")
                .SetPosition("Manager")
                .At(1000)
                .Build();

            WriteLine(employee);
            ReadKey();
        }
    }
}