在每次调用中重用幸存的局部变量。乌布？

Question

我是 C# 新手。我遇到了这样的代码示例：

namespace App1
{
    delegate int Sum(int number);

    class TestAnonymusMethod
    {
        static Sum m()
        {
            int result = 0;  // is not zeroed between calls

            Sum del = delegate (int number)
            {
                for (int i = 0;  i <= number;  i++)
                    result += i;
                return result;
            };
            return del;
        }

        static void Main()
        {
            Sum del1 = m();

            for (int i = 1;  i <= 5;  i++)
                Console.WriteLine("Sum of {0} == {1}", i, del1(i));

            Console.ReadKey();
        }
    }
}

输出为：

Sum of 1 == 1
Sum of 2 == 4
Sum of 3 == 10
Sum of 4 == 20
Sum of 5 == 35

如您所见，局部变量 result 不会在两次调用之间归零。是"undefined behaviour"吗？看起来它的发生是因为当 result 的范围关闭时，它的生命周期是未定义的。

但是在 C# 中重用活动实体的规则是什么？是规则 - "to reuse always"，还是在某些情况下，将创建新的而不是重复使用幸存的旧的？

Answer 1

Is it "undefined behavior"?

不，这是定义明确的行为 - 只是不是您期望的行为。

Looks like it happens because of when scope of result is closed, its life time is undefined.

不，result 的生命周期超出了 m() 的范围。来自 C# 5 规范第 7.15.5.1 节：

When an outer variable is referenced by an anonymous function, the outer variable is said to have been captured by the anonymous function. Ordinarily, the lifetime of a local variable is limited to execution of the block or statement with which it is associated (§5.1.7). However, the lifetime of a captured outer variable is extended at least until the delegate or expression tree created from the anonymous function becomes eligible for garbage collection.

在每次调用中重用幸存的局部变量。乌布？

Reusing of survived local variable in each call. UB?

c#

delegates

anonymous-function

undefined-behavior