Add Difference Between Slice And Pointer To Slice as a Go TIL

go/difference-between-slice-and-pointer-to-slice.md

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+# Difference Between Slice And Pointer To Slice
+
+Though a slice can be thought of and used as a flexible, variable-length
+array-like data structure, it is important to understand that it is also a
+special kind of pointer to an underlying array.
+
+This matters when we a function receives a slice versus a pointer to a slice as
+an argument, depending on what it is doing with that slice.
+
+If the function is access or updating elements in the slice, there is no
+difference. There is no meaningful difference between these two functions and
+we might as well use the former.
+
+```go
+func replaceAtIndex(slice []string, index int, value string) {
+	slice[index] = value
+}
+
+func replaceAtIndexPtr(slice *[]string, index int, value string) {
+	(*slice)[index] = value
+}
+```
+
+On the other hand, if the receiving function needs to append to or replace the
+slice, then we need to pass a pointer to the slice. A direct slice argument
+will result in only the function-local copy getting replaced.
+
+```go
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	s1 := []int{8, 6, 7, 9}
+	s2 := []int{8, 6, 7, 9}
+
+	addItem(s1, 11)
+	fmt.Printf("s1: %v\n", s1) //=> s1: [8 6 7 9]
+
+	addItemPtr(&s2, 11)
+	fmt.Printf("s2: %v\n", s2) //=> s2: [8 6 7 9 11]
+}
+
+func addItem(slice []int, value int) {
+	slice = append(slice, value)
+}
+
+func addItemPtr(slice *[]int, value int) {
+	(*slice) = append(*slice, value)
+}
+```
+
+[source](https://go.dev/tour/moretypes/8)