c＃7.0：开启System.Type [英] c# 7.0: switch on System.Type

问题描述

没有现有的问题可以回答这个问题。

No existing question has an answer to this question.

在c＃7中，我可以直接在 System.Type 上切换吗？ ？

In c# 7, can I switch directly on a System.Type?

当我尝试：

    switch (Type)
    {
      case typeof(int):
        break;
    }

它告诉我 typeof（int）必须是一个常量表达式。

it tells me that typeof(int) needs to be a constant expression.

是否有一些语法糖可以让我避免直接​​使用 case nameof（int）：比较平等的类型？ case语句中的 nameof（T）并不完全好，因为名称空间。因此，尽管名称冲突可能不适用于 int ，但它将适用于其他比较。

Is there some syntatic sugar that allows me to avoid case nameof(int): and directly compare the types for equality? nameof(T) in a case statement is not completely good because namespaces. So although name collision is probably not be applicable for int, it will be applicable for other comparisons.

换句话说，我m尝试比此类型更安全：

In other words, I'm trying to be more type-safe than this:

    switch (Type.Name)
    {
      case nameof(Int32):
      case nameof(Decimal):
        this.value = Math.Max(Math.Min(0, Maximum), Minimum); // enforce minimum 
        break;
    }

推荐答案

（已链接）新模式匹配功能允许这样做。

The (already linked) new pattern matching feature allows this.

通常，您需要打开一个值：

Ordinarily, you'd switch on a value:

switch (this.value) {
  case int intValue:
    this.value = Math.Max(Math.Min(intValue, Maximum), Minimum);
    break;
  case decimal decimalValue:
    this.value = Math.Max(Math.Min(decimalValue, Maximum), Minimum);
    break;
}

但是您可以使用它来打开一个类型类型：

But you can use it to switch on a type, if all you have is a type:

switch (type) {
  case Type intType when intType == typeof(int):
  case Type decimalType when decimalType == typeof(decimal):
    this.value = Math.Max(Math.Min(this.value, Maximum), Minimum);
    break;
}

请注意，这不是该功能的目的，因此可读性降低比传统的 if ... else if ... else if ... else 链，无论如何，传统链都是编译后的。我不建议使用这种模式匹配。

Note that this is not what the feature is intended for, it becomes less readable than a traditional if...else if...else if...else chain, and the traditional chain is what it compiles to anyway. I do not recommend using pattern matching like this.

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