What is New in C# 12

Tue, 10 Mar 2026 15:55:34 +0800

Primary constructors

One major feature in C# 12 is primary constructors. A primary constructor is declared on the type declaration instead of inside the class body. Its parameters can be used directly in members.

Record types

public record Address(string FirstName, string LastName);

Class types

public class Person(string firstName, string lastName)
{
 public override string ToString()
 {
 return $"{firstName},{lastName}";
 }
}

public Person(string firstName) : this(firstName, "hello")
{

}

Collection expressions

C# 12 adds collection expressions for concise collection initialization.

// Create an array:
int[] a = [1, 2, 3, 4, 5, 6, 7, 8];

// Create a list:
List<string> b = ["one", "two", "three"];

// Create a span
Span<char> c = ['a', 'b', 'c', 'd', 'e', 'f', 'h', 'i'];

// Create a jagged 2D array:
int[][] twoD = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];

// Create a jagged 2D array from variables:
int[] row0 = [1, 2, 3];
int[] row1 = [4, 5, 6];
int[] row2 = [7, 8, 9];
int[][] twoDFromVariables = [row0, row1, row2];

Range and index usage