Capacity Adjustments when Appending to Nil Slices

In Go, initializing a slice with nil results in an empty slice with zero length and zero capacity. When an element is subsequently appended to a nil slice, the capacity increases by two.

Capacity Expansion for Performance Optimization

Despite requesting only one element for the slice, Go may allocate more capacity than necessary to enhance performance. This reduces the frequency of memory allocations and copying operations required to expand the slice later.

Capacity as Upper Index Bound

Go's slice capacity defines the upper index bound for accessing elements. While the length of the slice represents the number of initialized elements, the capacity represents the maximum number of elements that can be stored without triggering a reallocation.

Zero Padding Beyond Length

As a consequence of the capacity exceeding the length, accessing elements beyond the length may return unexpected values, such as zeros. However, these values are not actually part of the slice.

Focus on Length for Practical Use

While capacity serves as an optimization tool, it's generally more practical to focus on the length of the slice for most purposes. Capacity information is primarily useful for performance optimization scenarios.