C# Feature – Collection expressions

Overview

Collection expressions use [..] to create arrays and collections and spread elements.

Introduced In

C# 12 (2023)

Before

var a = new int[] { 1, 2, 3 };

After

int[] a = [1, 2, 3];
int[] b = [..a, 4, 5];

Gotchas & Best Practices

• Requires target type; spreads copy elements.