Go Arrays vs Slices – Key Differences and Performance Tips

Arrays in Go

An array has a fixed size defined at compile time and cannot grow or shrink.

var arr [5]int = [5]int{1, 2, 3, 4, 5}
fmt.Println(len(arr)) // 5

Slices in Go

A slice is a dynamically-sized, flexible view into an underlying array, and is far more commonly used than arrays in everyday Go code.

nums := []int{1, 2, 3}
nums = append(nums, 4) // grows dynamically
fmt.Println(nums)      // [1 2 3 4]

Key Differences

• Size: arrays have a fixed size; slices can grow using append().
• Usage: slices are far more common in idiomatic Go code due to their flexibility.
• Memory: a slice is a small struct (pointer, length, capacity) referencing an underlying array, making it efficient to pass around.

Performance Tip

Pre-allocating slice capacity with make([]int, 0, 100) avoids repeated reallocations when you know the approximate size in advance.