Initialize elements with brackets like Lists in c#

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Category:Languages

I was thinking about arrays and lists and wondering if and how classes can get an implementation to be initializable like them. Let's take this class as basis:

class TestClass {     private List<int> Numbers = new List<int> ();      // Insert code here } 

What I would like to be able to do is to take the given values and internally fill my list.

TestClass test = new TestClass () { 2, 4, 7, 10 }; 

What would be normally possible is this:

List<int> test = new List<int> () { 2, 4, 7, 10 }; 

But I would like to have it for my own custom classes. The next question, which is optional, is if the same can be done for this syntax:

TestClass test = { 2, 4, 7, 10 }; 

I assume that is less likely to be possible. Note, these are different from this:

Cat cat = new Cat() { Name = "Sylvester", Age=8 }; 

These are direct and optional declarations of internal fields and properties.

See also MSDN for more info.

 


As stated here, collection initialisers will work on any class that implements IEnumerable and has an Add() method.

class TestClass : IEnumerable<int> {     private List<int> Numbers = new List<int> ();      public void Add(int n)     {         Numbers.Add(n);     }      // implement IEnumerable methods down here ...      public IEnumerator<int> GetEnumerator() => Numbers.GetEnumerator();      // etc ... } 

Note that if you have more than one parameter in your Add() method signature, then you can enclose them in curly braces to use collection initialiser syntax.

class TestClass2 : IEnumerable<(int, int)> {     private List<int> Numbers = new List<(int, int)> ();      public void Add(int x, int y)     {         Numbers.Add((x, y));     }      // implement IEnumerable methods down here ...      public IEnumerator<(int, int)> GetEnumerator() => Numbers.GetEnumerator();      // etc ... } 

Would be used like this:

var test = new TestClass2 { {2, 3}, {4, 5} }; 

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