A group blog from members of the VB team
For previous articles in this series please see
Sorry for the long delay between posts here. We're getting Orcas out the door and getting this series completed takes a back seat to shipping.
Originally I wanted to talk about looping structures next. However when I started writing that post I realized that I had to talk about lifetime before the looping structures would make sense.
Prior to Orcas the lifetime of a variable in VB was the entire function. This presented several problems from a closures perspective. Imagine you had a looping structure and the value was used in a lambda expression.
Dim list As New List(Of Func(Of Integer))
For i = 0 To 5
Dim x = i * 2
If True Then
For Each f In list
Console.Write(f() & " ")
In this example if we left the lifetime rules unchanged, there would be a single variable "x" for the entire function. That means that we would end up printing out
10 10 10 10 10
This is somewhat unexpected and essentially means that VB could not support complex Lambda scenarios. To fix this we altered the lifetime of variables to be tied to the scope they were contained in. The end effect is that each iteration of the loop has a separate "x" since each iteration enters and leaves the scope of the "if" statement. As a result it will print out
0 2 4 6 8 10
We did make one backcompat adjustment for this change. The lifetime of variables in VB was visible if you tried to use an uninitialized variable in a loop/goto. For instance the following code will also print out 0 2 4 6 8 10 because it takes advantage of the fact that the variable "x" has a lifetime longer than the loop.
For i = 0 To 5
Dim x As Integer
x += 2
To make sure that we didn't break any existing code we had one little errata for the change. When a variable's scope is re-entered, and hence recreated, and it is not initialized to a value it will get the last value of the variable.
Jared Parsons (http://blogs.msdn.com/jaredpar )
Thanks Jared! You offer insight to both the future and the past.
I am pleased to announce the release of new open-source software in vb6 that provides simulated Warren Buffett responses in basic investing. Bud Labitan and Greg Binning have combined their open sourced vb code and investing workbook into a free software application called archbot. Archbot A.I. open-source software combined with xml brainfiles provides simulated Warren Buffett like responses to your typed questions on investing. All the files, including support and source code are in one 27 MB download here:
http://www.frips.com/setup1.exe We welcome comments and volunteers who are motivated to enhance and make this free project even better.
If you wish to discuss this project, feel free to call me at 219-677-6281.
For previous articles in the series please see Part 1: Introduction Part 2: Method Calls Part 3: Scope
One of my favorite new features for Code Analysis in Visual Studio 2008 is our support for analyzing