Go: What is the difference between slice and array?

Array — fixed-length, value-type, length is part of the type. Slice — dynamic reference type backed by an array.

Arrays copy on assignment. This makes them safe from shared-state bugs but expensive for large sizes.

1arr := [3]int{1, 2, 3}
2copy := arr      // full copy
3copy[0] = 99
4fmt.Println(arr[0])  // 1 — unchanged

Slices share backing memory. Multiple slices can reference the same array, and mutations propagate. append may reallocate.

1xs := []int{1, 2, 3, 4}
2sub := xs[1:3]  // shares array
3sub[0] = 200    // mutates xs[1] too
4xs = append(xs, 5)  // may reallocate

When to use:

• Array — small fixed buffers, map keys, constants.
• Slice — default for all sequences.

Common mistakes:

• Not capturing append result.
• Unexpected mutations via shared backing arrays.
• Passing large arrays by value.
• Comparing slices with ==.