I’ve been learning some of the new features in C#12 and .Net 8.0 and came across 'collection expressions’. I tried to run a few code samples in the latest versions of Fire and Water (target framework set to .Net 8.0) but with no luck. I’m able to run the same code in Rider IDE, Visual Studio 2022 and from the command line (eg. dotnet run) 
‘IDE0028: Use collection initializers or expressions’ documentation
‘IDE0300: Use Collection Expression for Array’ documentation
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace CollectionExpression_CS1
{
static class Program
{
public static Int32 Main(string[] args)
{
//===================== Tradtional way pre C#12 ========================//
Console.WriteLine("The magic happens here.");
// Array:
int[] myArray1 = new int[] { 10, 20, 30, 40, 50 };
var myArray2 = new int[] { 10, 20, 30, 40, 50 };
// List:
List<string> myList1 = new List<string> { "apple", "banana", "orange" };
var myList2 = new List<string> { "apple", "banana", "orange" };
// Span:
var array3 = new char[] { 'a', 'b', 'c', 'd', 'e' };
Span<char> mySpan1 = array3.AsSpan();
var mySpan2 = array3.AsSpan();
//===================== with Collection Expressions =====================//
// Array
int[] demoArray = [10, 20, 30, 40, 50];
// List
List<string> demoList = ["apple", "banana", "orange"];
// Span
Span<char> demoSpan = ['a', 'b', 'c', 'd', 'e'];
//=======================================================================//
int[] array1 = { 1, 2, 3 };
int[] array2 = [4, 5, 6]; // using collection expression
// Traditional way
int[] combined = new int[array1.Length + array2.Length];
Array.Copy(array1, 0, combined, 0, array1.Length);
Array.Copy(array2, 0, combined, array1.Length, array2.Length);
// Using collection expression initialization
int[] combined1 = [..array1, ..array2];
foreach( var elem in combined1)
Write(elem); // 123456
WriteLine();
return 0;
}
}
}
