How well do you know C#? Put your knowledge to the test in Bill Wagner’s C# Puzzlers video LiveLesson!

Bill Wagner’s C# Puzzlers exposes common misconceptions that developers have about the C# language. Misconceptions occur when developers are unclear about how language features interact. On other occasions, a lack of understanding about how a single features works, can stump and frustrate the most experienced developer.

Using the “Puzzler” format, Bill demonstrates these misconceptions using small code samples; he then explores different ways for you to modify the code until its behavior is correct. This collection of Puzzlers is divided into seven sections. Each section delves into the rules that govern aspects of the C# language that developers find most confusing:

I. Generics
II. Method Resolution
III. Named and Optional Parameters
IV. LINQ
V. Value and Reference Semantics
VI. Dynamic Programming in C#

The introductory puzzle introduces the format using a puzzle, and discusses some of the nuances of object construction.

I. Generics
Generics are still one of the most important aspects of the .NET environment and the C# language. So many of the features we use every day are built upon generics in one way or another. Generics are still a complicated feature. You must create code whose types are not known until runtime. The compiler must generate IL with minimal information about the actual types that will be represented by the type parameters. The JIT must convert that IL into executable code and plug in the real types for the type parameters. Finally, the meta data carried along must include information that enables reflection and other advanced techniques to work correctly.

Puzzle 1 - Operations on Generic Type Parameters
What information gets conveyed, and what information cannot get used when a real type is substituted for a type parameter?
Puzzle 2 - Generics and Specializations
What happens when you create overloads for generic methods?
Puzzle 3 - Generics and Variance
How do generics and arrays differ with respect to variance?
Puzzle 4 - Generics, Constraints and Overloads
How does the compile choose between different candidate generic methods?

II. Method Resolution
The rules that govern method resolution in C# are necessarily complex. The features the community has asked for and the team has implemented have only added more complexity to those rules with each new release of the C# language. If you want to be a strong C# developer, you need to have at least a working knowledge of these rules.
Puzzle 5 - Overloading base class methods
What happens when derived classes create overloads of base class methods?
Puzzle 6 - Overloaded methods and null parameters
How does the compiler resolve overloaded methods when you use null parameters?
Puzzle 7 - Overloaded methods and null parameters revisited
What if the overloaded parameter types are unrelated?
Puzzle 8 - Overloaded methods and null parameters and Generics

What if one of the methods is generic? III. Named and Optional Parameters
Named and optional parameters sound so simple at first examination. But this feature has significant implications on other features in the language. It also has significant implications on areas as fundamental as how parameters are passed to called methods.
Puzzle 9 - Optional parameters and constructors
When is a default constructor not a default constructor?
Puzzle 10 - Optional Parameters and Overloads
Which is the better match?
Puzzle 11- Evaluation of Named Parameters
When do parameters get evaluated? Why does it matter?

IV. LINQ
LINQ introduced totally new ways of constructing and organizing programs. There were new rules related to how you wrote algorithms. Those rules still cause developers confusion in some cases.
Puzzle 12 - Bound Variables
When are LINQ queries evaluated?
Puzzle 13 - Method calls in LINQ queries
How does LINQ process expressions and method calls?

V. Value and Reference Semantics
Reference types and value types behave differently in many important ways. They also behave the same in many other ways. It can be difficult to keep those differences in mind as you get too accustomed to the similarities.
Puzzle 14 - Value type Semantics
When does copying values hurt?
Puzzle 15 - Value types and events
What happens when value types receive event notifications?

VI. Dynamic Programming in C#
Dynamic extensions move many of the common tasks that were performed by the compiler to runtime libraries. The interplay between static and dynamic typing creates new complications in C# programs. This section discusses some of the most common ways where static and dynamic types interact in ways that can be surprising.
Puzzle 16 - Dynamic Types and Extension Methods
How do dynamic types interact with extension methods?
Puzzle 17 - Anonymous types and Dynamic Methods
Under what conditions can anonymous types be treated dynamically?
Puzzle 18- Creating Dynamic Types in C#
Why would you pick different ways to implement dynamic types?