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