[LINQ via C#] - [C# Features]
Take this Person type as an example:
public class Person{ public string Name { get; set; }
public int Age { get; set; }}Object initializer
Before C# 3.0, a Person object can be initialized like this:
Person person = new Person();person.Name = "Dixin";person.Age = 30;With object initializer syntactic sugar in C# 3.0+, above code can be more declarative:
Person person = new Person() { Name = "Dixin", Age = 30 };which is will be compiled to above imperative version..
Collection initializer
Similarly, before C# 3.0, a collection can be initialized like this:
Collection<Person> persons = new Collection<Person>();persons.Add(anna);persons.Add(brian);In C# 3.0+, there is syntactic sugar called collection initializer:
Collection<Person> persons = new Collection<Person>() { anna, brian };The compiler will look up the Add() method, and compile collection initializer to above imperative code.
To use the collection initializer, a collection must:
- Implement System.IEnumerable
- Has a Add() instance method or extension method; It takes at least one parameter, and its return value is ignored
The following example demonstrates the minimal requirement of collection initializer:
public class PersonCollection : IEnumerable{ public void Add(Person person) { }
public IEnumerator GetEnumerator() { throw new NotImplementedException(); }}If the Add() method takes more than one parameters, this syntax should be used:
Dictionary<string, int> persons = new Dictionary<string, int>() { { "Anna", 18 }, // Compiled to persons.Add("Mark", 18). { "Brian", 19 } // Compiled to persons.Add("Steven", 18). };Index initializer
Since C# 6.0, index initializer syntactic sugar makes C# indexer declarative too:
PersonDictionary persons = new PersonDictionary() { [Guid.NewGuid()] = new Person() { Name = "Dixin", Age = 30 } };And this is the minimal requirement of index initializer:
public class PersonDictionary{ public Person this[Guid id] { set { throw new NotImplementedException(); } }}