Add Add A Method To A Struct 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).
 
-_1531 TILs and counting..._
+_1532 TILs and counting..._
 
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@@ -398,6 +398,7 @@ _1531 TILs and counting..._
 ### Go
 
 - [Access Go Docs Offline](go/access-go-docs-offline.md)
+- [Add A Method To A Struct](go/add-a-method-to-a-struct.md)
 - [Build For A Specific OS And Architecture](go/build-for-a-specific-os-and-architecture.md)
 - [Combine Two Slices](go/combine-two-slices.md)
 - [Do Something N Times](go/do-something-n-times.md)

go/add-a-method-to-a-struct.md

@@ -0,0 +1,70 @@
+# Add A Method To A Struct
+
+Given a `struct` in Go, we can attach a method to that struct. Put another way,
+we can define a method whose receiver is that struct. Then with an instance of
+that struct, we can call the method.
+
+Let's say we are modeling a turtle that can move around a 2D grid. A turtle has
+a heading (the direction it is headed) and a location (its current X,Y
+coordinate).
+
+```go
+type Heading string
+
+const (
+	UP    Heading = "UP"
+	RIGHT Heading = "RIGHT"
+	DOWN  Heading = "DOWN"
+	LEFT  Heading = "LEFT"
+)
+
+type Turtle struct {
+	Direction Heading
+	X         int
+	Y         int
+}
+```
+
+We can then add a method like so by specifying the receiver as the first part
+of the declaration:
+
+```go
+func (turtle *Turtle) TurnRight() {
+	switch turtle.Direction {
+	case UP:
+		turtle.Direction = RIGHT
+	case RIGHT:
+		turtle.Direction = DOWN
+	case DOWN:
+		turtle.Direction = LEFT
+	case LEFT:
+		turtle.Direction = UP
+	}
+}
+```
+
+The receiver is a pointer to a `Turtle`. The method is called `TurnRight`.
+There are no parameters or return values.
+
+Here are a sequence of calls to demonstrate how it works:
+
+```go
+func main() {
+	turtle := Turtle{UP, 5, 5}
+
+	fmt.Println("Turtle Direction:", turtle.Direction)
+	//=> Turtle Direction: UP
+
+	turtle.TurnRight()
+
+	fmt.Println("Turtle Direction:", turtle.Direction)
+	//=> Turtle Direction: RIGHT
+
+	turtle.TurnRight()
+
+	fmt.Println("Turtle Direction:", turtle.Direction)
+	//=> Turtle Direction: DOWN
+}
+```
+
+[source](https://go.dev/tour/methods/1)