为什么在Lambda内引发C#7功能异常? [英] Why is throwing an exception inside lambda a C# 7 feature?

问题描述

此语句在VS2015中不编译，但在VS2017中:

This statement doesn't compile in VS2015, but does in VS2017:

var example = new Action( () => throw new Exception()

为了支持在labmda表达式内引发异常，labmdas的解析方式必须进行哪些更改?

What had to change in the way labmdas are parsed in order to support throwing an exception inside a labmda expression?

特别是因为如果我使用lambda主体，则VS2015非常高兴:

Especially because if I use a lambda body, VS2015 is perfectly happy:

我的问题类似于为什么不能我抛出了来自表情健全成员的异常吗?，但是我的问题是为什么.在需要扩展编译器的lambda中创建表达式树时会发生什么?

My question is similar to Why can't I throw exceptions from an expression-bodied member?, but my question, is why. What had to happen in the creation of an expression tree from a lambda that necessitated extending the compiler?

推荐答案

在C#6中，必须在()=> 后加上一个表达式.它可能是一个不产生任何值的表达式，例如对返回类型为 void 的返回值的方法的调用，但这仍然是一个表达式.

In C# 6, () => had to be followed by an expression. It could be an expression that did not produce any value, such a call to a method with a return type of void, but that's still an expression.

在C#6中， throw 只能出现在一条语句中.完整的引发新的Exception("test"); 是一条语句.请注意其中的分号.语法中没有任何东西可以单独支持抛出新的Exception("test")，分号是其中不可或缺的一部分.

In C# 6, throw could only appear in a statement. The complete throw new Exception("test"); is a statement. Note the semicolon in there. There was nothing in the grammar to support throw new Exception("test") on its own, the semicolon was an integral part of it.

因此，要使此功能正常运行，要么C#7要么必须允许()=> 之后的语句，而且需要支持某种形式的语句而无需终止; 或C#7将需要扩展表达式的定义，以允许 throw 出现在其中.后者是发生了什么.

Therefore, to get this to work, either C# 7 would have to allow statements after () => and would need to support a form of statements without the terminating ;, or C# 7 would need to extend the definition of an expression to allow throw to appear there. The latter is what happened.

这篇关于为什么在Lambda内引发C#7功能异常?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！