static void Main()
{
// * The DoubleApplication higher-order function is called,
// passing the Twice function as a parameter
Console.WriteLine(DoubleApplication(Twice, 3));
Person[] people = PersonPrintout.CreatePeopleRandomly();
// * A delegate is passed as a parameter
Algorithms.SortPeople(people, Person.CompareByAge);
Console.WriteLine("\nSorted by age:");
PersonPrintout.ShowPeople(people);
Algorithms.SortPeople(people, Person.CompareBySurnameAndName);
Console.WriteLine("\nSorted by surname and name:");
PersonPrintout.ShowPeople(people);
// * Delegate variables can be created
Algorithms.Comparison comparison;
comparison = Person.CompareByAge;
Console.WriteLine("\nThe two first people compared by age: {0}",
comparison(people[0], people[1]));
comparison = Person.CompareBySurnameAndName;
Console.WriteLine("The two first people compared by surname and name: {0}",
comparison(people[0], people[1]));
}
static void Main()
{
const int a = 2, b = 1;
// * Lambda expression, with explicit type declaration
Func <int, int, int> operation = (int p1, int p2) => { return(p1 + p2); };
Console.WriteLine("Addition : {0}", operation(a, b));
// * Lambda expression, with explicit type declaration
// * In case it is a simple return, both the "return" word and { } can be omitted
operation = (p1, p2) => p1 - p2;
Console.WriteLine("Subtraction: {0}", operation(a, b));
// * Let's use Predicate and Action
// * With one single parameter, () can be omitted
Predicate <int> isEven = n => n % 2 == 0;
Action <string> show;
if (isEven(a))
{
show = (str) => {
ConsoleColor color = Console.ForegroundColor;
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine(str);
Console.ForegroundColor = color;
}
}
;
else
{
show = Console.WriteLine;
}
show("Hello world!");
// * Higher-order function
Func <Func <int, int>, int, int> applyTwice = (f, n) => f(f(n));
Console.WriteLine("Double application of twice: {0}", applyTwice(n => n + n, 3));
Console.WriteLine("Double of twice in a single statement: {0}",
((Func <Func <int, int>, int, int>)((f, n) => f(f(n))))
(n => n + n, 3)
);
Person[] people = PersonPrintout.CreatePeopleRandomly();
// * A lambda function is passed as a paramter to a BCL method (FindAll)
Person[] beyond18 = Array.FindAll(people, person => person.Age >= 18);
// * The people array supports our ForEach method becase it is an extension method.
// * A lambda function (action) is passed as a parameter
beyond18.ForEach(person => Console.WriteLine(person));
}
static void Main()
{
const int a = 2, b = 1;
// * Anonymous delegates (methods)
Func <int, int, int> binaryOperation = delegate(int p1, int p2) { return(p1 + p2); };
Console.WriteLine("Addition: {0}", binaryOperation(a, b));
binaryOperation = delegate(int p1, int p2) { return(p1 - p2); };
Console.WriteLine("Subtraction: {0}", binaryOperation(a, b));
Func <int, int> twice = delegate(int n) { return(n + n); };
Func <Func <int, int>, int, int> twiceTwice = delegate(Func <int, int> f, int n) { return(f(f(n))); };
Console.WriteLine("Twice twice: {0}", twiceTwice(twice, 3));
// In just one statement
Console.WriteLine("Twice twice in just one statement: {0}",
((Func <Func <int, int>, int, int>) // cast
(delegate(Func <int, int> f, int n) { return(f(f(n))); }) // twiceTwice
) // end of cast
( // the twiceTwice delegate is invoked
delegate(int n) { return(n + n); }, // first parameter (Funct<int,int>)
3 // second parameter (int)
) // end of invocation
);
Predicate <int> isEven = delegate(int n) { return(n % 2 == 0); };
Action <string> show;
if (isEven(a))
{
show = delegate(string str) {
ConsoleColor color = Console.ForegroundColor;
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine(str);
Console.ForegroundColor = color;
}
}
;
else
{
show = Console.WriteLine;
}
show("Hello world!");
Person[] people = PersonPrintout.CreatePeopleRandomly();
Person[] beyond18 = Array.FindAll(people, delegate(Person p) { return(p.Age >= 18); });
beyond18.ForEach(delegate(Person p) { Console.WriteLine(p); });
}
static void Main()
{
const int a = 2, b = 1;
// * A delegate variable using a user defined type
BinaryOperation operation = Program.Add;
Console.WriteLine("Addition: {0}", operation(a, b));
operation = Program.Sub;
Console.WriteLine("Subtraction: {0}", operation(a, b));
// * A delegate variable using a predefined type
Func <int, int, int> function = Program.Add;
Console.WriteLine("Addition: {0}", function(a, b));
function = Program.Sub;
Console.WriteLine("Subtaction: {0}", function(a, b));
// * The DoubleApplication higher-order function is called,
// passing another Twice (Func<int,int>) funcion as a parameter
Console.WriteLine("Double application of twice: {0}", DoubleApplication(Twice, 3));
// * Two more variables of predefined delegate types
Predicate <int> isEven = Program.IsEven;
Action <string> show;
if (isEven(a))
{
show = Program.ShowInRed;
}
else
{
show = Console.WriteLine;
}
show("Hello world!");
// * A BCL higher-order method (FindAll) is called,
// passing a predicate delegate as a parameter
Person[] people = PersonPrintout.CreatePeopleRandomly();
Person[] beyond18 = Array.FindAll(people, Program.PersonAge18OrBeyond);
beyond18.ForEach(Console.WriteLine);
}
