Go language slice index: Why doesn't single-element slice interception go beyond the bounds?

Detailed explanation of Go slicing indexing mechanism: The reason why single-element slice interception does not cross the boundary

Slicing in Go is a flexible dynamic array whose indexing behavior is sometimes different from traditional arrays. This article will explore in-depth the characteristics of Go slice indexing, especially why single-element slice interception does not cause out-of-bounds errors.

Consider the following code:

 func main() {
    arr := []int{7}
    s := arr[1:]
    fmt.Println(s) // Output[]
}

This code defines an integer slice arr containing a single element 7 and tries to intercept a new slice s from index 1. Intuitively speaking, index 1 is beyond the valid range of arr (only index 0), and it seems that an error should be reported. However, the program outputs an empty slice [] and no error occurred.

This is because the slices in Go use half-open interval representation. [i:j] means the element starting from index i and before index j (not including j ). Therefore, arr[1:] represents all elements starting from index 1 to the end of the slice. Since arr has only one element and no elements after index 1, the result is an empty slice.

This behavior is consistent with interception of multi-element slices. For example:

 func main() {
    arr := []int{7, 2}
    s := arr[:2] // is equivalent to arr[0:2]
    fmt.Println(s) // Output [7 2]
}

arr[:2] represents the element before index 0 to index 2, that is, elements 7 and 2 containing index 0 and 1.

If Go does not allow intercepting from indexes that are beyond the slicing range, then we cannot easily get empty slices. Empty slices are useful in many scenarios, so the design of Go language is reasonable. arr[1:] Although it seems that the index is out of bounds, under the slicing mechanism of Go, it is correctly interpreted as a subslicing from index 1 to the end, and the result is an empty slice, which is not an error. This design ensures simplicity and flexibility of slice operations.

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