在这种情况下，为什么不报告“切片范围超出范围”？ [重复]

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This question already has an answer here:

• Why does go allow slicing from len(slice)? 3 answers

Here's the code to reproduce:

package main

import "fmt"

func main() {
    var v []int
    v = append(v,1)
    v = append(v,v[1:]...)
    fmt.Println("hi", v)

}

v[1] will report index out of range, but v[1:]... won't, why?

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Answer 1

That's how spec defines slice expressions

For arrays or strings, the indices are in range if 0 <= low <= high <= len(a), otherwise they are out of range. For slices, the upper index bound is the slice capacity cap(a) rather than the length.

https://golang.org/ref/spec#Slice_expressions

And that's how index expressions for slices are defined

the index x is in range if 0 <= x < len(a), otherwise it is out of range

if x is out of range at run time, a run-time panic occurs

https://golang.org/ref/spec#Index_expressions

For your example:

v[1] panics because it's our of range as per the definition above (because 1 does not qualify the 0 <= x < len(a) reqirement)

v[1:] runs fine because it's identical to v[1:len(v)] and fits the if 0 <= low <= high <= cap(a) requirement.