Using C# 5 caller info attributes when targeting earlier versions of the .NET framework

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Caller info attributes are one of the new features of C# 5. They’re attributes applied to optional method parameters that enable you to pass caller information implicitly to a method. I’m not sure that description is very clear, so an example will help you understand:

        static void Log(
            string message,
            [CallerMemberName] string memberName = null,
            [CallerFilePath] string filePath = null,
            [CallerLineNumber] int lineNumber = 0)
        {
            Console.WriteLine(
                "[{0:g} - {1} - {2} - line {3}] {4}",
                DateTime.UtcNow,
                memberName,
                filePath,
                lineNumber,
                message);
        }

The method above takes several parameters intended to pass information about the caller: calling member name, source file path and line number. The Caller* attributes make the compiler pass the appropriate values automatically, so you don’t have to specify the values for these parameters:

        static void Foo()
        {
            Log("Hello world");
            // Equivalent to:
            // Log("Hello world", "Foo", @"C:\x\y\z\Program.cs", 18);
        }

This is of course especially useful for logging methods…

Notice that the Caller* attributes are defined in the .NET Framework 4.5. Now, suppose we use Visual Studio 2012 to target an earlier framework version (e.g. 4.0): the caller info attributes don’t exist in 4.0, so we can’t use them… But wait! What if we could trick the compiler into thinking the attributes exist? Let’s define our own attributes, taking care to put them in the namespace where the compiler expects them:

namespace System.Runtime.CompilerServices
{
    [AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false, Inherited = false)]
    public class CallerMemberNameAttribute : Attribute
    {
    }

    [AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false, Inherited = false)]
    public class CallerFilePathAttribute : Attribute
    {
    }

    [AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false, Inherited = false)]
    public class CallerLineNumberAttribute : Attribute
    {
    }
}

If we compile and run the program, we can see that our custom attributes are taken into account by the compiler. So they don’t have to be defined in mscorlib.dll like the “real” ones, they just have to be in the right namespace, and the compiler accepts them. This enables us to use this cool feature when targeting .NET 4.0, 3.5 or even 2.0!

Note that a similar trick enabled the creation of extension methods when targeting .NET 2.0 with the C# 3 compiler: you just had to create an ExtensionAttribute class in the System.Runtime.CompilerServices namespace, and the compiler would pick it up. This is also what enabled LinqBridge to work.

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Little known new features in Visual Studio 2012

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Visual Studio 2012 RC is out since last week, and even though I didn’t have much time to play with it yet, I think I like it so far. Lots of things have already been said about the design, and about the most important new features, but there are also many smaller and less remarkable improvements that make life easier for us. Since I have seen little or nothing written about those, I thought I would make a list of what I noticed so far.

Better Edit and Continue: improved debug experience with anonymous methods

Edit and continue is a very useful feature that has been present in Visual Studio for a long time. It’s great when you need to fix some code in the middle of a step-by-step debugging session without restarting the application completely. This feature has always had a limitation: you couldn’t use it in a method that contained an anonymous method:

Modifying a ’method’ which contains a lambda expression will prevent the debug session from continuing while Edit and Continue is enabled.

Before .NET 3.5, it wasn’t really a problem since anonymous methods were not very common, but since Linq was introduced and lambda expressions became more widely used, this limitation began to grow more and more annoying.

Well, good news: Visual Studio 2012 fixed that! You can now use Edit and Continue in a method that contains lambda expressions or Linq queries. Note that the limitation hasn’t completely disappeared: you still can’t modify a statement that contains an anonymous method. Note the slightly different error message:

Modifying a statement which contains a lambda expression will prevent the debug session from continuing while Edit and Continue is enabled.

But you can modify everything else in the method body, which is a great improvement. Note that editing a method that contains anonymous types is also supported, as long as you don’t modify the anonymous type itself.

Optimized event handler autocompletion

Visual Studio has a nice autocompletion feature that allow you to generate an event handler automatically when you type += and Tab after an event name :

image

But the new EventHandler(…) part is redundant, because since C# 2, method groups are implicitly convertible to compatible delegate types. Visual Studio 2012 fixes this and generates the shorter form:

image

OK, this is a very small change, but the previous behavior was really annoying me… I had actually suggested this improvement on Connect, so I’m glad to see that it was implemented.

Improved Find/Replace

The Find dialog in Visual Studio had not seen any improvement for as long as I can remember (probably since VS2003 or VS2005), so it was time for a change… In VS2012, it has been replaced with the Quick Find feature from the Productivity Power Tools extension. It appears as a small panel in the top right corner of the text editor, much less obtrusive than the old dialog:

image

It provides the following features:

  • incremental search (matches are highlighted as you type in the search box)
  • quick access to options such as match case, match whole word, or regex through the search field dropdown
  • support for .NET regular expressions (the old Find dialog was using a different kind of regex, not fully compatible with the .NET regex syntax)

If for some reason you need the full Find dialog, it’s still there: there’s a menu item to access it in the search field dropdown.

Quick launch

Where’s that command again? In the Debug menu or the Project menu? I can’t remember, and I don’t know the keyboard shortcut…

Sounds familiar? For me it does… Visual Studio has so many features that sometimes it can be hard to find what you’re looking for. That’s why the new Quick Access feature is a very welcome addition; it appears as a search box in the top right corner of the IDE, and allows you to type what you want to do:

image

Again, this feature comes from the Productivity Power Tools extension, and has been included in Visual Studio itself. It has also been given a more prominent place in the IDE (in VS2010 it was only accessible through the Ctrl+Q shortcut).

Smarter Solution Explorer

The Solution Explorer used to show only the files in your project, but nothing about what was in the files; If you want to see the classes and members, you had to switch to the Class View. Visual Studio 2012 changes that: now you can see what is declared in a file, just by expanding the node in the Solution Explorer:

image

This feature had been in Eclipse for a long time, so it was time for Visual Studio to catch up Clignement d'œil.

A few other interesting features of the new Solution Explorer:

  • Scope to This: allows to re-root the tree to a specific node (e.g. if you want to see only the content of a folder). The re-rooted tree can be viewed in a separate view.
  • Pending Changes Filter: show only pending changes (if source control is active for the current project)
  • Open Files Filter: show only open files
  • Sync With Active Document: quickly locate the current document in the Solution Explorer (very useful for large solutions)

And yes, that’s yet another feature that comes from Productivity Power Tools (it was known as the Solution Navigator), with a few improvements.

ALL CAPS MENUS

Menus in VS2012 are in ALL CAPS, and it’s not exactly the most popular change… there has been tons of negative feedback about this! Frankly, I’m a bit surprised that people pay so much importance to such an insignificant detail, when there are so many more important things to discuss. Personally, I found it a bit unsettling when I saw the first screenshots, but when I got my hands on the RC I found that it didn’t bother me at all. I guess most people will just get used to it in the end…

Anyway, the reason I mention this is to say that if you really don’t like the ALL CAPS menus, you can get the normal casing back with a simple registry tweak. Just open regedit, go to the HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\11.0\General key, create a DWORD value named SuppressUppercaseConversion and set it to 1.

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