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

Besides it’s not BP (catching-routing) – but this is the best isolation I can get.
But I get nice waves telling me “danger, danger – might be uninitialized”.
How comes?

Edit:
Please do not suggest “Simply put a string foo = string.Empty; at the ‘declaration'”. I’d like to declare it, but just do the assignment on time!

Answer 1

Some background from the C# specification (5.3.3.14):

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.

Edit 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
  }
}

I just thought of an example that shows the problem better:

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