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

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1558 TILs and counting..._
+_1559 TILs and counting..._
 
 See some of the other learning resources I work on:
 - [Ruby Operator Lookup](https://www.visualmode.dev/ruby-operators)
@@ -416,6 +416,7 @@ See some of the other learning resources I work on:
 - [Create A Slice From An Array](go/create-a-slice-from-an-array.md)
 - [Detect If Stdin Comes From A Redirect](go/detect-if-stdin-comes-from-a-redirect.md)
 - [Deterministically Seed A Random Number Generator](go/deterministically-seed-a-random-number-generator.md)
+- [Difference Between Slice And Pointer To Slice](go/difference-between-slice-and-pointer-to-slice.md)
 - [Do Something N Times](go/do-something-n-times.md)
 - [Find Executables Installed By Go](go/find-executables-installed-by-go.md)
 - [Format Date And Time With Time Constants](go/format-date-and-time-with-time-constants.md)

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

@@ -0,0 +1,55 @@
+# 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)