Collection expressions try to unify all syntaxes for initializing different collections. With them you can use the same syntax to express collections in a consistent way.
They replace all of this:
// all these versions are equivalent - the compiler generates identical code for each version
var numbers1 = new int[3] {1, 2, 3};
var numbers2 = new int[] {1, 2, 3};
var numbers3 = new[] {1, 2, 3};
int[] numbers4 = {1, 2, 3};
Using the new collection expressions (they cannot be used with var. You must declare the type)
// create an array
int[] intArray = [1, 2, 3, 4, 5];
// create empty array
int[] emptyArray = [];
// create a list
List<char> charList = ['D', 'a', 'v', 'i', 'd'];
// create a 2D list
List<int> int2dList = [[1, 2, 3], [4, 5, 6,], [7, 8, 9]];
how to flatten collections
int[] row0 = [1, 2, 3];
int[] row1 = [4, 5, 6];
int[] flattenCollection = [.. row0, 100, .. row1];
foreach(element in flattenCollection)
{
Console.Write($"{element}, ");
}
// 1, 2, 3, 100, 4, 5, 6,
Reference(s)
https://devblogs.microsoft.com/dotnet/refactor-your-code-with-collection-expressions/
https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-12#collection-expressions