C# List definition, parentheses vs curly braces

Question

I\'ve just noticed that when you declare a List in c# you can put parentheses or curly braces at the end.

List myList = new List&l         


        

Answer 1

The use of curly braces { } is called a collection initializer. For types that implement IEnumerable the Add method would be invoked normally, on your behalf:

List myList2 = new List() { "one", "two", "three" };

Empty collection initializers are allowed:

List myList2 = new List() { };

And, when implementing an initializer, you may omit the parenthesis () for the default constructor:

List myList2 = new List { };

You can do something similar for class properties, but then it's called an object initializer.

var person = new Person
                 {
                     Name = "Alice",
                     Age = 25
                 };

And its possible to combine these:

var people = new List
                 {
                     new Person
                         {
                             Name = "Alice",
                             Age = 25
                         },
                     new Person
                         {
                             Name = "Bob"
                         }
                 };

This language feature introduced in C# 3.0 also supports initializing anonymous types, which is especially useful in LINQ query expressions:

var person = new { Name = "Alice" };

They also work with arrays, but you can further omit the type which is inferred from the first element:

var myArray = new [] { "one", "two", "three" };

And initializing multi-dimensional arrays goes something like this:

var myArray = new string [,] { { "a1", "b1" }, { "a2", "b2" }, ... };

Update

Since C# 6.0, you can also use an index initializer. Here's an example of that:

var myDictionary = new Dictionary
                       {
                           ["one"] = 1,
                           ["two"] = 2,
                           ["three"] = 3
                       };