Fun with lambda expressions
Download as PPTX, PDF2 likes1,167 views
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)
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