Arrays, value copies, and shared references

The idea

C# distinguishes value types from reference types. Assigning an int copies its value; assigning an array variable copies a reference to the same array. A struct is a value type, but a struct containing a reference-type field still copies that reference. This makes the ownership of nested data more important than the label on the outer type.

An array clone creates a new array container. It does not recursively clone reference-type elements. Before claiming that a function preserves its input, identify every mutable object it may reach and decide which ones must be copied. For a rectangular array, GetLength(dimension) describes each dimension, while Length counts all elements. Keep loop bounds tied to the appropriate dimension rather than assuming a square grid.

using System;
int[] a = {2, 4};
int[] alias = a;
int[] copy = (int[])a.Clone();
alias[0] = 8;
copy[1] = 9;
Console.WriteLine($"{a[0]} {a[1]} {copy[0]} {copy[1]}");

8 4 2 9

The alias shares a, while the clone contains independent integer elements.