A story about JIT-x86 inlining and starg

Sometimes you can learn a lot during reading source .NET. Let's open the source code of a Decimal constructor from .NET Reference Source (mscorlib/system/decimal.cs,158):

// Constructs a Decimal from an integer value.
public Decimal(int value) {
    //  JIT today can't inline methods that contains "starg" opcode.
    //  For more details, see DevDiv Bugs 81184: x86 JIT CQ: Removing the inline striction of "starg".
    int value_copy = value;
    if (value_copy >= 0) {
        flags = 0;
    else {
        flags = SignMask;
        value_copy = -value_copy;
    lo = value_copy;
    mid = 0;
    hi = 0;

The comment states that JIT-x86 can't apply the inlining optimization for a method that contains the starg IL-opcode. Curious, is not it?

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About UTF-8 conversions in Mono

This post is a logical continuation of the Jon Skeet's blog post “When is a string not a string?”. Jon showed very interesting things about behavior of ill-formed Unicode strings in .NET. I wondered about how similar examples will work on Mono. And I have got very interesting results.

Experiment 1: Compilation

Let's take the Jon's code with a small modification. We will just add text null check in DumpString:

using System;
using System.ComponentModel;
using System.Text;
using System.Linq;
class Test
    const string Value = "X\ud800Y";
    static void Main()
        var description = (DescriptionAttribute)typeof(Test).
            GetCustomAttributes(typeof(DescriptionAttribute), true)[0];
        DumpString("Attribute", description.Description);
        DumpString("Constant", Value);
    static void DumpString(string name, string text)
        Console.Write("{0}: ", name);
        if (text != null)
            var utf16 = text.Select(c => ((uint) c).ToString("x4"));
            Console.WriteLine(string.Join(" ", utf16));

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Happy Monday!

Today I tell you a story about one tricky bug. The bug is a tricky one because it doesn't allow me to debug my application on Mondays. I'm serious right now: the debug mode doesn't work every Monday. Furthermore, the bug literally tell me: "Happy Monday!".

So, the story. It was a wonderful Sunday evening, no signs of trouble. We planned to release a new version of our software (a minor one, but it includes some useful features). Midnight on the clock. Suddenly, I came up with the idea that we have a minor bug that should be fixed. It requires a few lines of code and 10 minutes to do it. And I decided to write needed logic before I go to sleep. I open VisualStudio, lunch build, and wait. But something goes wrong, because I get the following error:

Error connecting to the pipe server.

Hmm. It is a strange error.

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To Refactor Or Not To Refactor?

I like refactoring. No, I love refactoring. No, not even like this. I awfully love refactoring.

I hate bad code and bad architecture. I feel quite creepy when I design a new feature and the near-by class contains absolute mess. I just can’t look at the sadly-looking variables. Sometimes before falling asleep I close my eyes and imagine what could be improved in the project. Sometimes I wake up at 3:00AM and go to my computer to improve something. I want to have not just code, but a masterpiece that is pleasant to look at, that is pleasant to work with at any stage of the project.

If you just a little bit share my feelings we have something to talk about. The matter is that over some time something inside me began to hint that it’s a bad idea to refactor all code, everywhere and all the time. Understand me correctly – code should be good (even better when it’s ideal), but in real life it’s not reasonable to improve code instantly. I formed some rules about the refactoring timeliness. If I am itching to improve something, I look at these rules and think “Is that the moment when I need to refactor the code?” So, let’s talk about when refactoring is necessary and when it’s inappropriate.

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Strange behavior of FindElementsInHostCoordinates in WinRT

Silverlight features a splendid method: VisualTreeHelper.FindElementsInHostCoordinates. It allows the HitTest, i.e. makes it possible for a point or rectangle to search for all visual sub-tree objects that intersect this rectangle or point. Formally the same method VisualTreeHelper.FindElementsInHostCoordinates is available in WinRT. And it seems the method looks in the same way, but there is a little nuance. It works differently in different versions of the platform. So, let’s see what’s going on.

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About System.Drawing.Color and operator ==

Operator == that allows easy comparison of your objects is overridden for many standard structures in .NET. Unfortunately, not every developer really knows what is actually compared when working with this wonderful operator. This brief blog post will show the comparison logic based on a sample of System.Drawing.Color. What do you think the following code will get:

var redName = Color.Red;
var redArgb = Color.FromArgb(255, 255, 0, 0);
Console.WriteLine(redName == redArgb);

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Setting up build configuration in .NET

You get two default build configurations: Debug and Release, when creating a new project in Visual Studio. And it’s enough for most small projects. But there can appear a necessity to extend it with the additional configurations. It’s ok if you need to add just a couple of new settings, but what if there are tens of such settings? And what if your solution contains 20 projects that need setting up of these configurations? In this case it becomes quite difficult to manage and modify build parameters.

In this article, we will review a way to make this process simpler by reducing description of the build configurations.

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Jon Skeet's Quiz

Jon Skeet was once asked to give three questions to check how well you know C#. He asked the following questions:

  • Q1. What constructor call can you write such that this prints True (at least on the Microsoft .NET implementation)?
object x = new /* fill in code here */;
object y = new /* fill in code here */;
Console.WriteLine(x == y);

Note that it’s just a constructor call, and you can’t change the type of the variables.

  • Q2. How can you make this code compile such that it calls three different method overloads?
void Foo()
  • Q3. With a local variable (so no changing the variable value cunningly), how can you make this code fail on the second line?
string text = x.ToString(); // No exception
Type type = x.GetType(); // Bang!

These questions seemed interesting to me, that is why I decided to discuss the solutions.

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To Add Comments or Not to Add?

A really good comment is the one you managed to avoid. (c) Uncle Bob

Lately, I’ve been feeling really tired of hot discussions on if it’s necessary to add comments in the code. As a rule, there are self-confident juniors with the indisputable statement as: “Why not to comment it, it will be unreadable without the comments!” on one side. And experienced seniors are on the other side. They understand that if it’s possible to go without the comments than “You better, damn it, do it in this way!” Probably, many developers got comment cravings since they’ve been students when professors made them comment every code line, “to make the student better understand it”. Real projects shouldn’t contain a lot of comments that only spoil the code. I don’t agitate for avoiding comments at all, but if you managed to write the code that doesn’t need comments, you can consider it your small victory. I would like to refer you to some good books that helped form my position. I like and respect these authors and completely share their opinion.

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Perfect code and real projects

I’ve got a problem. I am a perfectionist. I like perfect code. This is not only the correct way to develop applications but also the real proficiency. I enjoy reading a good listing not less than reading a good book. Developing architecture of a big project is no simpler than designing architecture of a big building. In case the work is good the result is no less beautiful. I am sometimes fascinated by how elegantly the patterns are entwined in the perfect software system. I am delighted by the attention to details when every method is so simple and understandable that can be a classic sample of the perfect code.

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