Hidden Features of C#? [closed]

Question

This came to my mind after I learned the following from this question:

where T : struct

We, C# developers, all know the basics of C#. I mean declarations, conditionals, loops, operators, etc.

Some of us even mastered the stuff like Generics, anonymous types, lambdas, LINQ, ...

But what are the most hidden features or tricks of C# that even C# fans, addicts, experts barely know?

Here are the revealed features so far:

Keywords

• yield by Michael Stum
• var by Michael Stum
• using() statement by kokos
• readonly by kokos
• as by Mike Stone
• as / is by Ed Swangren
• as / is (improved) by Rocketpants
• default by deathofrats
• global:: by pzycoman
• using() blocks by AlexCuse
• volatile by Jakub Šturc
• extern alias by Jakub Šturc

Attributes

• DefaultValueAttribute by Michael Stum
• ObsoleteAttribute by DannySmurf
• DebuggerDisplayAttribute by Stu
• DebuggerBrowsable and DebuggerStepThrough by bdukes
• ThreadStaticAttribute by marxidad
• FlagsAttribute by Martin Clarke
• ConditionalAttribute by AndrewBurns

Syntax

• ?? (coalesce nulls) operator by kokos
• Number flaggings by Nick Berardi
• where T:new by Lars Mæhlum
• Implicit generics by Keith
• One-parameter lambdas by Keith
• Auto properties by Keith
• Namespace aliases by Keith
• Verbatim string literals with @ by Patrick
• enum values by lfoust
• @variablenames by marxidad
• event operators by marxidad
• Format string brackets by Portman
• Property accessor accessibility modifiers by xanadont
• Conditional (ternary) operator (?:) by JasonS
• checked and unchecked operators by Binoj Antony
• implicit and explicit operators by Flory

Language Features

• Nullable types by Brad Barker
• Anonymous types by Keith
• __makeref __reftype __refvalue by Judah Himango
• Object initializers by lomaxx
• Format strings by David in Dakota
• Extension Methods by marxidad
• partial methods by Jon Erickson
• Preprocessor directives by John Asbeck
• DEBUG pre-processor directive by Robert Durgin
• Operator overloading by SefBkn
• Type inferrence by chakrit
• Boolean operators taken to next level by Rob Gough
• Pass value-type variable as interface without boxing by Roman Boiko
• Programmatically determine declared variable type by Roman Boiko
• Static Constructors by Chris
• Easier-on-the-eyes / condensed ORM-mapping using LINQ by roosteronacid
• __arglist by Zac Bowling

Visual Studio Features

• Select block of text in editor by Himadri
• Snippets by DannySmurf

Framework

• TransactionScope by KiwiBastard
• DependantTransaction by KiwiBastard
• Nullable<T> by IainMH
• Mutex by Diago
• System.IO.Path by ageektrapped
• WeakReference by Juan Manuel

Methods and Properties

• String.IsNullOrEmpty() method by KiwiBastard
• List.ForEach() method by KiwiBastard
• BeginInvoke(), EndInvoke() methods by Will Dean
• Nullable<T>.HasValue and Nullable<T>.Value properties by Rismo
• GetValueOrDefault method by John Sheehan

Tips & Tricks

• Nice method for event handlers by Andreas H.R. Nilsson
• Uppercase comparisons by John
• Access anonymous types without reflection by dp
• A quick way to lazily instantiate collection properties by Will
• JavaScript-like anonymous inline-functions by roosteronacid

Other

• netmodules by kokos
• LINQBridge by Duncan Smart
• Parallel Extensions by Joel Coehoorn

Answer 1

@Ed, I'm a bit reticent about posting this as it's little more than nitpicking. However, I would point out that in your code sample:

MyClass c;
  if (obj is MyClass)
    c = obj as MyClass

If you're going to use 'is', why follow it up with a safe cast using 'as'? If you've ascertained that obj is indeed MyClass, a bog-standard cast:

c = (MyClass)obj

...is never going to fail.

Similarly, you could just say:

MyClass c = obj as MyClass;
if(c != null)
{
   ...
}

I don't know enough about .NET's innards to be sure, but my instincts tell me that this would cut a maximum of two type casts operations down to a maximum of one. It's hardly likely to break the processing bank either way; personally, I think the latter form looks cleaner too.

Answer 2

Maybe not an advanced technique, but one I see all the time that drives me crazy:

if (x == 1)
{
   x = 2;
}
else
{
   x = 3;
}

can be condensed to:

x = (x==1) ? 2 : 3;

Answer 3

This one is not "hidden" so much as it is misnamed.

A lot of attention is paid to the algorithms "map", "reduce", and "filter". What most people don't realize is that .NET 3.5 added all three of these algorithms, but it gave them very SQL-ish names, based on the fact that they're part of LINQ.

"map" => Select
Transforms data from one form into another

"reduce" => Aggregate
Aggregates values into a single result

"filter" => Where
Filters data based on a criteria

The ability to use LINQ to do inline work on collections that used to take iteration and conditionals can be incredibly valuable. It's worth learning how all the LINQ extension methods can help make your code much more compact and maintainable.

Answer 4

Attributes in general, but most of all DebuggerDisplay. Saves you years.

Answer 5

Everything else, plus

1) implicit generics (why only on methods and not on classes?)

void GenericMethod<T>( T input ) { ... }

//Infer type, so
GenericMethod<int>(23); //You don't need the <>.
GenericMethod(23);      //Is enough.

2) simple lambdas with one parameter:

x => x.ToString() //simplify so many calls

3) anonymous types and initialisers:

//Duck-typed: works with any .Add method.
var colours = new Dictionary<string, string> {
    { "red", "#ff0000" },
    { "green", "#00ff00" },
    { "blue", "#0000ff" }
};

int[] arrayOfInt = { 1, 2, 3, 4, 5 };

---

Another one:

4) Auto properties can have different scopes:

public int MyId { get; private set; }

---

Thanks @pzycoman for reminding me:

5) Namespace aliases (not that you're likely to need this particular distinction):

using web = System.Web.UI.WebControls;
using win = System.Windows.Forms;

web::Control aWebControl = new web::Control();
win::Control aFormControl = new win::Control();

Answer 6

Here are some interesting hidden C# features, in the form of undocumented C# keywords:

__makeref

__reftype

__refvalue

__arglist

These are undocumented C# keywords (even Visual Studio recognizes them!) that were added to for a more efficient boxing/unboxing prior to generics. They work in coordination with the System.TypedReference struct.

There's also __arglist, which is used for variable length parameter lists.

One thing folks don't know much about is System.WeakReference -- a very useful class that keeps track of an object but still allows the garbage collector to collect it.

The most useful "hidden" feature would be the yield return keyword. It's not really hidden, but a lot of folks don't know about it. LINQ is built atop this; it allows for delay-executed queries by generating a state machine under the hood. Raymond Chen recently posted about the internal, gritty details.