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+---
+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.