问题描述
虽然最好只抛出从 std :: exception 类派生的类型的异常，但是C ++可以抛出任何东西。以下所有示例都是有效的C ++：
While it is good practice to throw only exceptions of types derived from std::exception class, C++ makes it possible to throw anything. All below examples are valid C++:
throw "foo"; // throws an instance of const char*
throw 5; // throws an instance of int
struct {} anon;
throw anon; // throws an instance of not-named structure
throw []{}; // throws a lambda!
最后一个例子很有趣，因为它可能允许传递某些代码以在捕获站点执行，而不必定义一个单独的类或函数。
The last example is interesting, as it potentially allows passing some code to execute at catch site without having to define a separate class or function.
但是捕获lambda（或闭包）有没有可能？ 捕获（[] {} e）不起作用。
But is it at all possible to catch a lambda (or a closure)? catch ([]{} e) does not work.
推荐答案
异常处理程序是根据类型进行匹配的，与将异常对象匹配到处理程序的隐式转换相比，在其他上下文中的限制更大。
Exception handlers are matched based on type, and the implicit conversions done to match an exception object to a handler are more limited than in other contexts.
每个lambda表达式都会引入一个闭包类型是周围范围唯一的。因此，您的幼稚尝试无法成功，因为 [] {} 在throw表达式和处理程序中具有完全不同的类型！
Each lambda expression introduces a closure type that is unique to the surrounding scope. So your naive attempt cannot work, for []{} has an entirely different type in the throw expression and the handler!
但是你是对的。 C ++允许您抛出任何对象。因此，如果您事先将lambda显式转换为与异常处理程序匹配的类型，它将允许您调用该任意可调用对象。例如：
But you are correct. C++ allows you to throw any object. So if you explicitly convert the lambda before-hand to a type that matches an exception handler, it will allow you to call that arbitrary callable. For instance:
try {
throw std::function<void()>{ []{} }; // Note the explicit conversion
} catch(std::function<void()> const& f) {
f();
}
这可能有有趣的用途，但是我要小心，不要扔掉没有得到的东西来自 std :: exception 。更好的选择可能是创建一个从 std :: exception 派生并可以容纳可调用类型的类型。
This may have interesting utility, but I'd caution against throwing things not derived from std::exception. A better option would probably be to create a type that derives from std::exception and can hold a callable.
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