36 lines
1.0 KiB
Markdown
36 lines
1.0 KiB
Markdown
|
---
|
||
|
|
title: "Golang's append mutates the provided array"
|
||
|
|
date: 2020-10-30T12:49:37+01:00
|
||
|
|
draft: false
|
||
|
|
tags:
|
||
|
|
- golang
|
||
|
|
images:
|
||
|
|
- /images/golang-append.gif
|
||
|
|
---
|
||
|
|
|
||
|
|
A word of warning when using `append()` in Golang...
|
||
|
|
|
||
|
|
When using a slice of an array as the first parameter when calling `append` if the length of the resulting array is less than that of the initial array then the values in the initial array will be overridden by the new values being appended.
|
||
|
|
|
||
|
|
For example, if we use `append` to take the first two values from the array called `first` and all the values from the array called `second` we can see that `first` is being mutated unexpectedly.
|
||
|
|
|
||
|
|
```go
|
||
|
|
package main
|
||
|
|
|
||
|
|
import "fmt"
|
||
|
|
|
||
|
|
func main() {
|
||
|
|
first := []int{0, 1, 2, 3, 4, 5, 6}
|
||
|
|
second := []int{4, 5, 6}
|
||
|
|
|
||
|
|
fmt.Println(first)
|
||
|
|
// -> [0 1 2 3 4 5 6]
|
||
|
|
fmt.Println(append(first[:2], second...))
|
||
|
|
// -> [0 1 4 5 6]
|
||
|
|
fmt.Println(first)
|
||
|
|
// -> [0 1 4 5 6 4 5 6]
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
This is _only_ an issue when the resulting array is shorter than the array passed in as the first parameter.
|