Why Does Slicing a Go Slice Reduce Capacity Sometimes, But Not Always?

Understanding Slice Capacity Decrease After Slicing

In Go, a slice is a flexible data structure that represents a contiguous section of an underlying array. When you slice a slice, you create a new slice that refers to a subset of the original slice's data.

Why does s = s[2:] decrease capacity, while s = s[:4] and s = s[:0] do not?

The line s = s[:4] extends the slice's length to include the first four elements of the original slice. This does not change the capacity because the underlying array still has sufficient capacity to accommodate the extended slice.

On the other hand, s = s[:0] creates a slice with zero length. The capacity remains unchanged, as the underlying array still has capacity to hold the original elements.

However, s = s[2:] drops the first two elements of the slice. This creates a new slice that refers to the subset of the original slice starting at index 2. The capacity decreases because the new slice no longer has access to the first two elements.

Can you recover the first two elements after dropping them with s = s[2:]?

No, you cannot recover the first two elements after slicing them off with s = s[2:]. Slicing creates a new slice with a new pointer to the underlying array. When you drop elements from the beginning, the pointer is shifted to the new starting index, and the old elements are inaccessible.

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