visual studio failed to detect code return path

I experienced on when refactoring some code, maybe I'm blind but I failed to see why the following code won't work.

public bool Foo()
{
    try
    {
        return SomeFunctionMightThrow();
    }
    catch (Exception ex)
    {
        Logger.log开发者_如何学Python(ex);
        throw ex;
    }
}

So far so good, if I refactor code to

public bool Foo()
{
  try
  {
    return SomeFunctionMightThrow();
  }
  catch (Exception ex)
  {
    LogAndThrow(ex);
  }
}

private void LogAndThrow(Exception ex)
{
  Logger.log(ex);
  throw ex;
}

Code does not compile now.

You could potentially change it to...

public bool Foo()
{
  try
  {
    return SomeFunctionMightThrow();
  }
  catch (Exception ex)
  {
    // note: this will reset the exception stack trace
    throw LogAndReturnException(ex);
  }
}

private Exception LogAndReturnException(Exception ex)
{
  Logger.log(ex);
  return ex;
}

This essentially does exactly what you want but gives VS the code return path.

Or for a more simplistic approach which will retain the stack trace, just change your catch to:

catch (Exception ex)
{
  Log(ex);
  throw; // retains stack trace
}

The compiler doesn't take into account that your LogAndThrow() method always will throw an exception - that being the case all code paths in Foo() must return a boolean, so you could just do this:

public bool Foo()
{
  try
  {
    return SomeFunctionMightThrow();
  }
  catch (Exception ex)
  {
    LogAndThrow(ex);
    return false; //will never get here
  }
}

In general since you throw anyway I would recommend using a try/catch block at a single central spot in your app for logging, i.e. at the highest level unless you can really handle the exception - it doesn't look like you are here.