Initializing collections such as arrays, lists and spans can be verbose. This feature introduces a shorthand syntax for creating collections that uses square brackets [] instead of calling constructors.

Code

Now

char[] a = [ 'z', 'x', '4', '8' ];

List<string> l = ["one", "two", "three"];

Span<int> s = [1, 2, 3, 4, 5];

Span<char> c = [..myArray, 'k'];

Before

char[] a = new[] { 'z', 'x', '4', '8' };

List<string> l = new() { "one", "two", "three" };

Span<int> s = new[] { 1, 2, 3, 4, 5 };

Span<char> c = new(myArray.Append('k').ToArray());

Notes

• The spread element .. copies every item from any enumerable collection into the new one
• [] creates an empty collection of the target type
• Collection expressions have no natural type, so var x = [1, 2]; does not compile
• Collection expression arguments ^{C# 15.0} let you pass constructor arguments such as a capacity or comparer

More information

• What's new in C# 12.0
• Language reference