流利的接口和继承在C＃ [英] Fluent interfaces and inheritance in C#

问题描述

我将展示通过举例的一个问题。还有用流利接口的基类：

I'll show a problem by example. There is a base class with fluent interface:

class FluentPerson
{
    private string _FirstName = String.Empty;
    private string _LastName = String.Empty;

    public FluentPerson WithFirstName(string firstName)
    {
        _FirstName = firstName;
        return this;
    }

    public FluentPerson WithLastName(string lastName)
    {
        _LastName = lastName;
        return this;
    }

    public override string ToString()
    {
        return String.Format("First name: {0} last name: {1}", _FirstName, _LastName);
    }
}

和子类：

class FluentCustomer : FluentPerson
{
    private long _Id;

    private string _AccountNumber = String.Empty;

    public FluentCustomer WithAccountNumber(string accountNumber)
    {
        _AccountNumber = accountNumber;
        return this;
    }
    public FluentCustomer WithId(long id)
    {
        _Id = id;
        return this;
    }

    public override string ToString()
    {
        return base.ToString() + String.Format(" account number: {0} id: {1}", _AccountNumber, _Id);
    }
}

问题是，当你调用 customer.WithAccountNumber（000）。WithFirstName（约翰）。WithLastName（史密斯）可以不加 .WithId（123）到底，因为 WithLastName（）方法的返回类型FluentPerson（不FluentCustomer）。

The problem is that when you call customer.WithAccountNumber("000").WithFirstName("John").WithLastName("Smith") you can't add .WithId(123) in the end because return type of the WithLastName() method is FluentPerson (not FluentCustomer).

这个问题怎么解决，通常？

How this problem usually solved?

推荐答案

您可以使用泛型来实现这一目标。

You can use generics to achieve that.

public class FluentPerson<T>
    where T : FluentPerson<T>
{
    public T WithFirstName(string firstName)
    {
        // ...
        return (T)this;
    }

    public T WithLastName(string lastName)
    {
        // ...
        return (T)this;
    }
}

public class FluentCustomer : FluentPerson<FluentCustomer>
{
    public FluentCustomer WithAccountNumber(string accountNumber)
    {
        // ...
        return this;
    }
}

和现在：

var customer = new FluentCustomer()
  .WithAccountNumber("123")
  .WithFirstName("Abc")
  .WithLastName("Def")
  .ToString();

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