We all love LINQ in C#. Fosna will talk about advanced LINQ concepts like expression trees, how to build them, how to parse them, how to exploit them.

1. Road to Dynamic
LINQ
Vedran Maršić AKA Fosna
Warning: Expression Trees Ahead

2. About me
 Vedran Maršić AKA Fosna
 dev at http://www.axilis.com/author/vmarsic/
 organizing programming workshops for kids
 Logo, Scratch, HTML, CSS, JavaScript, Python, C++

3. We’ll cover
 Part 1
 What is expression tree in C#
 How is it different from similar looking lambda delegates
 How to build expression trees
 How to parse expression trees
 Where are you already using them
 Part 2
 Check out few expression tree exploits
 Point to brilliant, not easy to understand, ideas or projects from some cool developer
maniacs 

4. We won’t cover
 Implementing LINQ providers
 Implementing deep copy
 Implementing faster static dictionary
 Implementing IoC container

5. Introduction to Expression
Trees

6. Expression Tree Nodes
Plain old C#
• c = a + b
Lambda expression
• (a, b) => a + b
Gists:
AddStatement.linq
SimpleBinaryExpression.linq

7. Definition
 represent code in a tree-like data structure
 not in MSIL (Microsoft Intermediate Language)
 each node is an expression
 has compiler smell all over it
 can compile to get functions!
 get some good ol’ MSIL
 MSIL ex:
IL_0007: ldloc.0 // a
IL_0008: ldloc.1 // b
IL_0009: add
IL_000A: stloc.2 // c

8. History
 Came with .NET 3.5
 Built some muscle in .NET 4.0
 ‘nuff said 

9. Expression Tree Dissection
x => x < 5
Gist: SimpleLogicalExpression.linq

10. Why Expression Tree?
analyze expression tree
discover what you want done
decide how to do it

11. Expression Trees Vs Lambda Delegates
One lambda expression
(a, b) => a + b

12. Expression Trees Vs Lambda Delegates
One lambda expression
(a, b) => a + b
Two type signatures

13. Expression Trees Vs Lambda Delegates
...
Gist: TreeVsDelegate.linq

14. Applied Expression Trees Vs Lambda Delegates
 Which technology exploits expression trees and which one doesn’t?
 LINQ to Objects
 LINQ to Entities (EF)
 LINQ to XML
 Parallel LINQ

15. How to Create an Expression Tree?
 From lambda expression at compile time
 Method invocation flavor
 Query syntax
 Using Expression API at run time
 Why would anyone do that?
Gist: BuildExp.linq

16. Famous Extension Methods
...attached to Clever Interfaces

17. Lazy: AsEnumerable()
 If code can be executed in process then the job can be done with the
simple type called IEnumerable<T>
 remember yield return

18. Lazy: AsQueryable()
 If you need to translate a query expression into a string that will be passed
to another process, then use IQueryable<T> and expression trees.

19. Eager Extension Methods
• ToList()
• ToArray()
• ToDictionary()
• ToLookup()
• First()
• FirstOrDefault()
• Single()
• SingleOrDefault()

20. Applied Expression Trees
Next time...

21. Thanks. Bye!
No questions, right?

22. Resources
 Start with
 http://stackoverflow.com/a/403233/953338
 Expression Tree Basics, Charlie Calvert 31 Jan 2008 3:49 AM
 http://blogs.msdn.com/b/charlie/archive/2008/01/31/expression-tree-basics.aspx
 Published by Olexander Ivanitskyi on Tuesday, June 11, 2013
 LINQ: Func<T> vs. Expression<Func<T>>
 http://ivanitskyi.blogspot.hr/2013/06/linq-func-vs-expression.html
 asked Apr 27 '09 at 13:50, Richard Nagle
 Why would you use Expression<Func<T>> rather than Func<T>?
 http://stackoverflow.com/questions/793571/why-would-you-use-expressionfunct-
rather-than-funct

23. Resources
 C# 6.0 Features
 https://github.com/dotnet/roslyn/wiki/New-Language-Features-in-C%23-6
 Canonical Functions
 https://msdn.microsoft.com/en-us/library/vstudio/bb738626(v=vs.100).aspx
 The .NET Programmer’s Playground - LinqPad
 http://www.linqpad.net/