有没有比这更好的选择来“打开类型"? [英] Is there a better alternative than this to 'switch on type'?

问题描述

看到 C# 不能 switch 类型(我收集的不是作为特殊情况添加的，因为 is 关系意味着不止一个不同的 case 可能适用)，有没有更好的方法来模拟除此之外的类型的切换?

Seeing as C# can't switch on a Type (which I gather wasn't added as a special case because is relationships mean that more than one distinct case might apply), is there a better way to simulate switching on type other than this?

void Foo(object o)
{
    if (o is A)
    {
        ((A)o).Hop();
    }
    else if (o is B)
    {
        ((B)o).Skip();
    }
    else
    {
        throw new ArgumentException("Unexpected type: " + o.GetType());
    }
}

推荐答案

切换类型在 C# 中肯定是缺乏的(更新:在 C#7/VS 2017 中支持切换类型 - 见下面扎卡里耶茨的回答).为了在没有大的 if/else if/else 语句的情况下执行此操作，您需要使用不同的结构.不久前我写了一篇博文，详细介绍了如何构建 TypeSwitch 结构.

Switching on types is definitely lacking in C# (UPDATE: in C#7 / VS 2017 switching on types is supported - see Zachary Yates's answer below). In order to do this without a large if/else if/else statement, you'll need to work with a different structure. I wrote a blog post awhile back detailing how to build a TypeSwitch structure.

https://docs.microsoft.com/archive/blogs/jaredpar/开关类型

简短版本:TypeSwitch 旨在防止冗余转换并提供类似于普通 switch/case 语句的语法.例如，这里是 TypeSwitch 在标准 Windows 窗体事件上的作用

Short version: TypeSwitch is designed to prevent redundant casting and give a syntax that is similar to a normal switch/case statement. For example, here is TypeSwitch in action on a standard Windows form event

TypeSwitch.Do(
    sender,
    TypeSwitch.Case<Button>(() => textBox1.Text = "Hit a Button"),
    TypeSwitch.Case<CheckBox>(x => textBox1.Text = "Checkbox is " + x.Checked),
    TypeSwitch.Default(() => textBox1.Text = "Not sure what is hovered over"));

TypeSwitch 的代码实际上非常小，可以轻松地放入您的项目中.

The code for TypeSwitch is actually pretty small and can easily be put into your project.

static class TypeSwitch {
    public class CaseInfo {
        public bool IsDefault { get; set; }
        public Type Target { get; set; }
        public Action<object> Action { get; set; }
    }

    public static void Do(object source, params CaseInfo[] cases) {
        var type = source.GetType();
        foreach (var entry in cases) {
            if (entry.IsDefault || entry.Target.IsAssignableFrom(type)) {
                entry.Action(source);
                break;
            }
        }
    }

    public static CaseInfo Case<T>(Action action) {
        return new CaseInfo() {
            Action = x => action(),
            Target = typeof(T)
        };
    }

    public static CaseInfo Case<T>(Action<T> action) {
        return new CaseInfo() {
            Action = (x) => action((T)x),
            Target = typeof(T)
        };
    }

    public static CaseInfo Default(Action action) {
        return new CaseInfo() {
            Action = x => action(),
            IsDefault = true
        };
    }
}

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