Let's recap: a GUID is a 128 bit integer that is used as a globally unique identifier. GUIDs are not a security system; they do not guarantee uniqueness in a world where hostile parties are deliberately attempting to cause collisions; rather, they provide...

So how is it that a GUID can be guaranteed to be unique without some sort of central authority that ensures uniqueness, a la the ISBN system? Well, first off, notice that the number of possible GUIDs is vastly larger than the number of possible ISBNs...

What is a GUID? The acronym stands for "globally unique identifier"; GUIDs are also called UUIDs, which stands for "universally unique identifier". (It is unclear to me why we need two nigh-identical names for the same thing, but there you have it.) A...

Returning now to the subject at hand: we would like to allow user-defined "overloads" of the & and | operators in C#, and if we are going to have & and | be overloadable, it seems desirable to have && and || be overloadable too. But now...

Before we continue our exploration of truthiness in C#, a brief digression. I mentioned last time the "knights and knaves" puzzles of logician Raymond Smullyan. Though I do enjoy those puzzles, my favourite of his puzzles are his chess puzzles, and my...

In Raymond Smullyan 's delightful books about the Island of Knights and Knaves -- where, you'll recall, knights make only true statements and knaves make only false statements -- the knights and knaves are of course clever literary devices to explore...

The way you typically represent a "missing" or "invalid" value in C# is to use the "null" value of the type. Every reference type has a "null" value; that is, the reference that does not actually refer to anything. And every "normal" value type has a...

UPDATE: Whoops! I accidentally set a draft of this article to automatically publish on a day that I was away on vacation. The fact that it was (1) not purple and (2) introduced the topic and then stopped in mid-sentence were both clues that this was an...

You're probably all familiar with the feature of C# which disallows reading from a local variable before it has been "definitely assigned": void M() { int x; if (Q()) x = 123; if (R()) Console.WriteLine(x); // illegal! } This is illegal because there...

I am super excited to announce that the beta release of Visual Studio version 11 (which includes the .NET CLR version 4.5, Visual Basic version 11 and C# version 5) is available for download right now. As you know if you've been following our CTP releases...

The first time I ran my histogram visualizer I asked for a Cauchy distribution with a minimum of -10 and a maximum of 10, and of course I got a graph that looks much like the one from my article of last week: Looks perfectly reasonable; I guess my program...

My original version of the histogram-generating code that I whipped up for the previous episode of FAIC contained a subtle bug. Can you spot it without going back and reading the corrected code? private static int[] CreateHistogram(IEnumerable<double>...

When building simulations of real-world phenomena, or when generating test data for algorithms that will be consuming information from the real world, it is often highly desirable to produce pseudo-random data that conform to some nonuniform probability...

The standard way to teach beginner OO programmers about classes is to make a metaphor to the real world. And indeed, I do this all the time in this blog, usually to the animal kingdom. A "class" in real life codifies a commonality amongst a certain set...

"Late binding" is one of those computer-sciency terms that, like "strong typing", means different things to different people. I thought I might describe what the term means to me. First off, what is "binding"? We can't understand what it means to bind...

Today, yet another episode in my ongoing series " What's the difference? " This time, a non-computer-related topic . I am often complimented on my choice of outerwear in the Seattle rainy season, and I hate to respond to a well-meant compliment with a...

Last time I noted that any two usages of "the same" anonymous type within an assembly actually unify to be the same type. By "the same" we mean that the two anonymous types have the same property names and types, and that they appear in the same order...

Back in my last post of 2010 I said that I would do an example of anonymous types unifying within an assembly "in the new year". I meant 2011, but here we are "in the new year" again, so, no time like the present. The C# specification guarantees you that...

If you ask a dozen C# developers what a "local variable" is, you might get a dozen different answers. A common answer is of course that a local is "a storage location on the stack". But that is describing a local in terms of its implementation details;...

Here's an inconvenient truth: just about every "public surface area" change you make to your code is a potential breaking change. First off, I should clarify what I mean by a "breaking change" for the purposes of this article. If you provide a component...

Happy New Year all! It has just been brought to my attention that this blog and the Programmer Ryan Gosling photo blog share at least one reader: I admit it, I LOL'd. In the interests of total accuracy I'd like to point out that the first entry on the...

OK, let's finish up this year and this series. We have an algorithm that can compute what cells in the zero octant are in view to a viewer at the origin when given a function that determines whether a given cell is opaque or transparent. It marks the...

I hope you all had a pleasant Christmas and Boxing Day; we chose to not travel to see family this year and had a delightful time visiting friends. We'll finish up 2011 here with a bit more on shadowcasting, and then pick up with more C# language design...

Last time we saw how many different ways there were to get the calculation of the top cell based on the top vector wrong. Today we'll take a briefer look at determining the bottom cell. We know from our discussion of last time that the right way to determine...

Before we get started, thanks for all the great comments to the previous couple of posts. I'll be updating the algorithm to try to make even better-looking circles of light based on the comments. Like I said, there's a lot of subtleties to these algorithms...