Why Does My Go Code Throw a \"panic: runtime error: index out of range\" Error When the Array Length is Not Null?

"Go “panic: runtime error: index out of range” When the Length of Array is Not Null

Analysis

The provided Go code encounters a runtime error due to accessing an index beyond the allowed range. When working with slices in Go, it's crucial to understand the concept of capacity and length.

Understanding Slices

A Go slice is a descriptor of an array segment. It encompasses a pointer to the array, the length of the segment, and its capacity (maximum length of the segment).

make([]string, 0, 4) vs. make([]string, 4)

The make function initializes and allocates slices. result := make([]string, 0, 4) creates a slice with length 0 and capacity 4, while result := make([]string, 4) (or its equivalent result := []string{"", "", "", ""}) initializes a slice with both length and capacity 4.

Array Access

In result := make([]string, 0, 4), the underlying array is empty, so accessing result[0] will cause a runtime error. In contrast, result := make([]string, 4) has four string elements, allowing access to result[0], result[1], result[2], and result[3].

Resolution for Your Code

In your myFunc function, you use the problematic result := make([]string, 0, 4) initialization. Given that your code requires appending elements, you should consider using result := make([]string, 0) and append elements using the append function. Alternatively, you could use result := []string{} or result := make([]string, 4), depending on your specific requirements.

Here's a working version of your code using make([]string, 0) and append (The Go Playground):

<code class="go">package main

import "fmt"

func main() {
    fmt.Println(myFunc("Political srt"))
}

func myFunc(input string) []string {
    strs := strings.Fields(input)
    result := make([]string, 0) // Initialize with length 0 and append as needed
    for _, s := range strs {
        if strings.ContainsAny(s, "eaiu") {
            result = append(result, s) // Append to the result slice
        }
    }
    return result
}</code>

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