C# polymorphism methods dynamic-dispatch

基于变量值的动态方法调度

发布于 2024-08-13 13:20:32 字数 530 浏览 5 评论 0原文

长的 switch 语句常常会让人不悦。解决方案是使用多态性。但是，如果我打开的不是类型代码怎么办？我想做的是将 switch 语句替换为类似的内容...

public void HandleString(string s = "Hello")
{
 ...
}

public void HandleString(string s = "Goodbye")
{
 ...
}

...
HandleString("Hello"); // results in the first method being called.

这将替换以下内容...

string s = "Hello";

switch(s)
{
   case "Hello":
   ...
   break;
   case "Goodbye":
   ...
   break;
   default;
   break;
}

有什么想法吗？理论上，我认为您可以完全取消“if/switch”语句，而只调用根据表达式的值自动绑定的方法。

原文

Long switch statments are often frowned upon. The solution is to use polymorphism. However what if the thing I'm switching on is not a type code? What I would like to do is replace the switch statement with something like this...

public void HandleString(string s = "Hello")
{
 ...
}

public void HandleString(string s = "Goodbye")
{
 ...
}

...
HandleString("Hello"); // results in the first method being called.

This would replace the following...

string s = "Hello";

switch(s)
{
   case "Hello":
   ...
   break;
   case "Goodbye":
   ...
   break;
   default;
   break;
}

Any ideas? In theory I think you could do away with 'if/switch' statements altogether and just call methods that are automatically bound based on the value of an expression.

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请止步禁区 2024-08-20 13:20:32

如果您有大量选项，并且将来很有可能会有更多选项 - 或者您只需要系统易于扩展 - 那么您始终可以使用显式调度表：

Dictionary<string, Action<string>> actions =
    new Dictionary<string, Action<string>>()
    {
        { "Hello", HandleHello },
        { "Goodbye", HandleGoodbye }
    };

private static void HandleHello(string s) { ... }

private static void HandleGoodbye(string s) { ... }

...

actions[s](s);

您还可以提供一种扩展方法通过允许 API 的外部客户端为给定字符串注册自己的处理程序来创建表。

If you have a large number of options, and high possibility that there will be more in the future - or you just need to system to be easily extensible - then you can always use an explicit dispatch table:

Dictionary<string, Action<string>> actions =
    new Dictionary<string, Action<string>>()
    {
        { "Hello", HandleHello },
        { "Goodbye", HandleGoodbye }
    };

private static void HandleHello(string s) { ... }

private static void HandleGoodbye(string s) { ... }

...

actions[s](s);

You can also provide a way to extend the table by allowing external clients of your API to register their own handler for a given string.

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情话已封尘 2024-08-20 13:20:32

有些语言实现了这种语义。我熟悉的一个是来自 Phillips 的名为 Elegant 的编译器生成工具。

在这样的语言中，简单的阶乘算法可能如下所示：

fact (value : Int) : Int
    conditions value < 0
{
    { "Illegal input value\n" } astype Message
    return 0
}

fact (value = 0) : Int
{
    return 0
}

fact (value = 1) : Int
{
    return 1
}

fact (value : Int) : Int
{
    return value * fact(value - 1);
}

There are languages that implement that sort of semantics. One that I'm familiar with is the compiler generator tool called Elegant from Phillips.

In a language like this, a simple factorial algorithm might look like:

fact (value : Int) : Int
    conditions value < 0
{
    { "Illegal input value\n" } astype Message
    return 0
}

fact (value = 0) : Int
{
    return 0
}

fact (value = 1) : Int
{
    return 1
}

fact (value : Int) : Int
{
    return value * fact(value - 1);
}

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~没有更多了~