c# - 为什么我的变量仍然是 "uninitialized"？

Question

string foo;
try
{
    foo = "test"; // yeah, i know ...
}
catch // yeah, i know this one too :)
{
    foo = null;
}
finally
{
    Console.WriteLine(foo); // argh ... @#!
}
Console.WriteLine(foo); // but nothing to complain about here

除了它不是 BP(捕获路由)——但这是我能得到的最好的隔离。
但是我得到了很好的波浪告诉我“危险，危险 - 可能未初始化”。怎么来的？

编辑:
请不要建议“在‘声明’处简单地放置一个 string foo = string.Empty;”。我想申报，但按时完成作业即可!

Answer 1

C# 规范 (5.3.3.14) 的一些背景:

For a try statement stmt of the form:

try try-block finally finally-block

(...)

The definite assignment state of v at the beginning of finally-block is the same as the definite assignment state of v at the beginning of stmt.

编辑 Try-Catch-Finally(5.3.3.15):

Definite assignment analysis for a try-catch-finally statement (...) is done as if the statement were a try-finally statement enclosing a try-catch statement

The following example demonstrates how the different blocks of a try statement (§8.10) affect definite assignment.

class A
{
  static void F() 
  {
    int i, j;
    try {
      goto LABEL;
      // neither i nor j definitely assigned
      i = 1;
      // i definitely assigned
    }
    catch {
      // neither i nor j definitely assigned
      i = 3;
      // i definitely assigned
    }
    finally {
      // neither i nor j definitely assigned
      j = 5;
      // j definitely assigned
    }
    // i and j definitely assigned
    LABEL:;
    // j definitely assigned
  }
}

我只是想到了一个能更好地说明问题的例子:

int i;
try
{
    i = int.Parse("a");
}
catch
{
    i = int.Parse("b");
}
finally
{
   Console.Write(i);
}