Embedded Structs

Go is not an object-oriented language. However, embedded structs provide a kind of data-only inheritance that can be useful at times. Keep in mind, Go doesn't support classes or inheritance in the complete sense, embedded structs are just a way to elevate and share fields between struct definitions.

type car struct {
  make string
  model string
}

type truck struct {
  // "car" is embedded, so the definition of a
  // "truck" now also additionally contains all
  // of the fields of the car struct
  car
  bedSize int
}

Embedded vs nested

• An embedded struct's fields are accessed at the top level, unlike nested structs.
• Promoted fields can be accessed like normal fields except that they can't be used in composite literals

lanesTruck := truck{
  bedSize: 10,
  car: car{
    make: "toyota",
    model: "camry",
  },
}

fmt.Println(lanesTruck.bedSize)

// embedded fields promoted to the top-level
// instead of lanesTruck.car.make
fmt.Println(lanesTruck.make)
fmt.Println(lanesTruck.model)

Assignment

At Textio, a "user" struct represents an account holder, and a "sender" is just a "user" with some "sender" specific data. A "sender" is a user that has a rateLimit field that tells us how many messages they are allowed to send.

Fix the system by using an embedded struct as expected by the test code.