Introduction to LINQ and Lambda Expressions

1. Presented by: Andrew Gray Introduction to LINQand Lambda Expressions Introduction to LINQ and Lambda Expressions

2. About Me Andrew Gray • Developer • Current Work: Technical Test Engineer at McLane Advanced Technologies (Ranorex Studio/C#) • Hobbies: Music, Gaming, Indie Game Development • Game Engines: Torque, Unity Previous Works: http://andrewrgray.webs.com/games.html (Requires Unity Webplayer) Introduction to LINQ and Lambda Expressions

3. Agenda • What is LINQ? • Using LINQ • LINQ Considerations • What is a Lambda Expression? • Using Lambda Expressions • Lambda Considerations • Open Discussion • References • Conclusion Introduction to LINQ and Lambda Expressions

4. What is LINQ? • Acronym – Language-Integrated Query [1] • Purpose - Improvement in notation • Introduced in .NET 3.5 / Visual Studio 2008 • Provides SQL-like operations for searching in-memory data [2] • Often suggested by ReSharper when an IEnumerable is iterated over in a loop. No, not him... Introduction to LINQ and Lambda Expressions

5. Using LINQ – Standard Form • Create Query [2] • Execute the Query on a data source [3] using System.Core; // …Other Declarations… private static DataRow[] FindRowsInTable(DataTable table, string field, string value) { return (fromDataRow r intable.Rows where r[field].ToString() == value select r).ToArray(); } Introduction to LINQ and Lambda Expressions

6. Using LINQ - Parallelization • Parallelization in LINQ is achieved by adding .AsParallel() after the collection name. [4] • Parallel LINQ by default uses all cores up to 64, but can be limited by using .DegreeOfParallelism(int cores) [4] • Using PLINQ can yield a performance benefit for your application, as core usage can be controlled. [4] using System.Core; // …Other Declarations… private static DataRow[] FindRowsInTable(DataTable table, string field, string value) { return (fromDataRow r intable.Rows.AsParallel().WithDegreeOfParallelism(2) where r[field].ToString() == value select r).ToArray(); } Introduction to LINQ and Lambda Expressions

7. LINQ Considerations • Syntactic Sugar (Replaces for/foreach loop with SQL-like syntax) • Parallelization is possible – potential speed boost • Query execution is deferred from declaration • Additional methods have been added in the IQueryable interface • Code Smell: LINQ query on information read from a database • A SQL query is generally better • Some LINQ commands take Lambda Expressions as parameters Introduction to LINQ and Lambda Expressions

8. What is a Lambda Expression? • Origin – Anonymous Functions • Lambda Calculus (1936 – Alonzo Church) [5] • LISP (1957) [4] • Purpose • A refined way of defining anonymous methods or delegates • Implements “closures” in C# • Closure: “A function together with a referencing environment for the non-local variables of that function.” [6] • No/Limited tail-call optimization in C# • Language syntax is limited inside a Lambda What do you call a baby eigensheep? Introduction to LINQ and Lambda Expressions

9. Using Lambda Expressions • Lambdas take the form: (args[]) => { statements; } • Formally, => (lambda operator) reads as ‘[Left] goes to [Right]’ [7] • Lambdas accept a void parameter list. • () => statement(s); • Lambdas do not require arguments to refer to external variables • return isn’t required to get the result of a lambda, unless the value or reference of an internal variable is being returned. • Func<int, int> foo = a => { intb = 7; returna + b; } • As with delegates, anonymous methods are called by using the variable with the given parameters. • returnfoo(3); • The definition is not executed until it is called! Introduction to LINQ and Lambda Expressions

10. Using Lambda Expressions • Lambdas can be mapped to the first-class function (Func<[types]>) generic type • The last type in the generic is the return type; all types before that are argument types. • Provides a means of storing or returning Lambdas with strong typing • Lambdas can also be mapped to Action<[types]> • All parameters are inputs • Actions have a void return type. Introduction to LINQ and Lambda Expressions

11. Using Lambda Expressions • Keywords break, continue, and goto are not supported in Lambdas. [7] • The params keyword cannot be used in Func<> or the lambda’s parameter list. • params can be used with standard delegate declarations. • Optional parameters are not supported in Lambdas. • Func<int> foo(inta = 7) => a*a;Does not compile! • Cannot enclose ref or out parameters from the parent scope. [7] • Cannot be on the left side of is or as[7] • Lambdas in C# cannot be recursive like a named method Introduction to LINQ and Lambda Expressions

12. Using Lambda Expressions public class CoinExample { private const string _Heads = “Heads!”; private const string _Tails = “Tails!”; privateFunc<string> _Flip; privateFunc<string, string, string> _Tree; private void CoinFlipper() { Random generator = new Random(GetSeed()); _Flip = () => ((generator.Next() % 2) == 0) ? _Heads : _Tails; _Tree = (lhs, rhs) => lhs + “ x ” + rhs; Console.WriteLine(“Result: ” + _Tree(_Flip(),_Flip()); } } Introduction to LINQ and Lambda Expressions

13. Using Lambda Expressions – IQueryable • Lambda Expressions are often arguments in various IQueryable methods! • .Where(Func<bool>) • .Select(Func<bool>) privatestaticDataRowFoo(DataTable table, stringfindMe) { if (table == null || table.Rows.Count == 0) throw new ArgumentNullException(“table”); DataRow query = table.Where(a => a == findMe).GetFirstOrDefault(); return query; } Introduction to LINQ and Lambda Expressions

14. Using Lambda Expressions • Lambdas do not require arguments to refer to external variables Func<string> _Compare; private void Foo() { const inta = 7, b = 7; // With Lambda Expression… _Compare = () => a == b ? "Yes" : "No"; Console.WriteLine("Does A match B? " + _Compare()); // Normal way… Console.WriteLine(“Does A match B? “ + a == b ? “Yes” : “No”); } Introduction to LINQ and Lambda Expressions

15. Using Lambda Expressions • Lambdas can be modified after initial declaration, but ReSharper will show a warning for the modification! Func<bool> _Compare; private void Foo(int a, int b) { // Initial declaration _Compare = () => a == b; Console.WriteLine( “Does A match B? “ + _Compare() ? “Yes” : “No” ); _Compare = () => a > b; // Warning here! Console.WriteLine( “Is A greater than B? “ + _Compare() ? “Yes” : “No” ); } Introduction to LINQ and Lambda Expressions

16. Using Lambda Expressions • Lambda Expressions can help implement dependency injection. public classActionInjectionExample { private decimal _Primary; private decimal _Alt; public boolIsGreater { getBinaryCompare(() => _Primary > _Alt); } public boolIsLesser { getBinaryCompare(() => _Primary < _Alt); } public boolBinaryCompare(Func<bool> action) { // Implementation details… boolresult = action(); // Further details… return result; } } Introduction to LINQ and Lambda Expressions

17. Lambda Considerations • Pros • Provides support for first-class functions and expression trees • Useful as arguments to certain LINQ query operations. • Useful when a delegate will have a simple body. • Lambdas can help implement dependency injection. • Neutral • Lambdas defer execution until use. • Cons • Unsubscribing a Lambda from an event requires additional work. [9] • Variables used in a Lambda are not garbage collected until the referencing delegate goes out of scope. [6] • There is evidence that using local variables inside Lambdas can cause resource leaks. [8] • Variables that are not primitives are passed by reference. [10] Introduction to LINQ and Lambda Expressions

18. Open Discussion • Questions? • Past Experience? Introduction to LINQ and Lambda Expressions

19. References 1http://msdn.microsoft.com/en-us/library/bb397926.aspx (Introduction to LINQ) 2http://msdn.microsoft.com/en-us/library/bb397906.aspx (LINQ) 3http://stackoverflow.com/questions/1524813/convert-this-linq-expression-into-lambda (LINQ example) 4http://msdn.microsoft.com/en-us/library/dd997425.aspx (Introduction to PLINQ) 5http://en.wikipedia.org/wiki/Anonymous_function (Anonymous Function/Lambda Expression) 6http://en.wikipedia.org/wiki/Closure_(computer_science) (Lexical Closures) 7http://msdn.microsoft.com/en-us/library/bb397687.aspx (Lambda Expressions - MSDN) 8http://alookonthecode.blogspot.com/2011/05/lambda-expressions-anonymous-classes.html (Issues) 9http://www.h3mm3.com/2011/06/unsubscribing-to-events-in-c.html (Unsubscribing from Lambdas) 10http://msdn.microsoft.com/en-us/library/ms228360(v=vs.90).aspx (Passing Primitives / Classes) Introduction to LINQ and Lambda Expressions

20. Fin. Thank you for attending! andrew.russel.gray@gmail.com Introduction to LINQ and Lambda Expressions