Fun with lambda expressions
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This document provides an overview of lambda expressions in .NET and Java. It introduces lambda expressions and their origins in lambda calculus. Examples are given of using lambda expressions in C# and F# with LINQ and delegates. The evolution of delegates in C# is discussed, from using methods to anonymous methods to lambda expressions. Expression trees in C# are also covered. The differences between lambda expressions in C# and Java are highlighted, with examples given of sorting lists of objects using lambdas in each language. In summary, lambdas are unnamed inline functions that can be used anywhere a delegate is required to keep code encapsulated.
![C# Expression Trees
ParameterExpression num1 = Expression.Parameter(typeof(int), "num1");
ParameterExpression num2 = Expression.Parameter(typeof(int), "num2");
//Create the expression parameters
ParameterExpression[] parameters = new ParameterExpression[] { num1, num2 };
//Create the expression body
BinaryExpression body = Expression.Add(num1, num2);
//Create the expression
Expression<Func<int, int, int>> expression = Expression.Lambda<Func<int, int, int>>(body, parameters);
// Compile the expression
Func<int, int, int> compiledExpression = expression.Compile();
// Execute the expression.
int result = compiledExpression(3, 4); //return 7](https://image.slidesharecdn.com/funwithlambdaexpressions-150520013828-lva1-app6891/85/Fun-with-lambda-expressions-15-320.jpg)
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Fun with lambda expressions
- 1. Fun with Lambda Expressions Michael Melusky - @mrjavascript Central Penn .NET – Tuesday May 19 2015
- 2. About the Speaker Michael Melusky Software Engineer for Audacious Inquiry in Baltimore, MD Instructor at Penn State Harrisburg and ITT Technical Institute Enjoys cooking, baseball and video games
- 3. Motivation and goals for the talk I’m primarily a “Java Developer” by trade Lamda Expressions were newly added in Java SE 8 Overview of what lambda expressions are Overview of what delegates and anonymous methods are Show how anonymous methods differ from lambda expressions Show how the C# and Java implementations differ from each other
- 4. What is a Lambda A lambda is a function Originates from lambda calculus, expressing computation using variable binding and substitution A function is a computation which takes parameters and returns a value A lambda enables functions to be passed around or stored like data
- 5. Lambdas in .NET Popularized by LINQ (.NET language-integrated query) Example: Test Scores with LINQ Example: Even numbers in a list (C# with System.Linq.Enumerable) Example: Even numbers in a list (F#)
- 6. Functional Programming Paradigm Transition from imperative programming to functional programming “Not what to do but how to do it” Functions are first order data types C# produced the ability to create anonymous functions, inline statements or expressions whenever a delegate is expected
- 7. Evolution of C# Delegates In C# 1.0, delegates can be instantiated by initialized with a method defined in the code delegate void MyDelegate(string s); Static void Foo(string s) { Console.WriteLine(s); } MyDelegate del = new MyDelegate(Foo);
- 8. Evolution of C# Delegates C# 2.0 allowed for anonymous methods as a way to write inline blocks that could be executed in delegate invocation MyDelegate M = delegate(string s) { Console.WriteLine(s); }
- 9. Evolution of C# Delegates In C# 3.0 and above, delegates can now be initialized with a lambda expression: MyDelegate M = (x) => { Console.WriteLine(s) }; Example: Delegates in C#
- 10. C# Delegate Types Action<T> Delegate method that takes zero or more input parameters Does not return a type Func<TResult> Delegate method that takes zero or more input parameters Returns a value or reference Predicate<T> Delegate similar to Func except it returns a boolean
- 11. Lambda Expressions in C# Lambda expressions can be used with any delegate type in C# (input parameters) => expression
- 12. Lambda Expressions in C# Examples: (x, y) => x == y (int x, string s) => s.Length > x () => SomeMethod()
- 13. C# Expression Trees (a,b) => a+b; C# compiler translates lambda expressions into expression trees at MSIL time (Microsoft Intermediate Language) Expression<Func<int, int, int>> lambda = (a,b) => a + b;
- 14. C# Expression Trees Example: expression trees
- 15. C# Expression Trees ParameterExpression num1 = Expression.Parameter(typeof(int), "num1"); ParameterExpression num2 = Expression.Parameter(typeof(int), "num2"); //Create the expression parameters ParameterExpression[] parameters = new ParameterExpression[] { num1, num2 }; //Create the expression body BinaryExpression body = Expression.Add(num1, num2); //Create the expression Expression<Func<int, int, int>> expression = Expression.Lambda<Func<int, int, int>>(body, parameters); // Compile the expression Func<int, int, int> compiledExpression = expression.Compile(); // Execute the expression. int result = compiledExpression(3, 4); //return 7
- 16. Lambda Expressions in Java Recently added as a feature in Java SE 8 The following interfaces now support lambda: Iterable.forEach(lambda) Collection.removeIf(lambda) List.replaceAll(lambda) List.sort(lambda) Replaces Collections.sort()
- 17. Person Sort in Java Example: Sorting a list of objects using Comparator<T>
- 18. Person Sort in C# Example: Same example in C# using List.Sort(Comparison<T>)
- 19. In Summary Lambdas are unnamed, inline functions Lambda expressions can be used anywhere a delegate is required to keep your code encapsulated You can chain methods together to perform multiple operations In VB, you cannot use lambda expressions as action delegates
- 20. Questions? Thank you for coming. twitter/mrjavascript github/mrjavascript slideshare/mrjavascript