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Anonymous Structs in Go

An anonymous struct is just like a normal struct, but it is defined without a name and therefore cannot be referenced elsewhere in the code.

To create an anonymous struct, just instantiate the instance immediately using a second pair of brackets after declaring the type:

myCar := struct {
  brand string
  model string
} {
  brand: "Toyota",
  model: "Camry",
}

You can even nest anonymous structs as fields within other structs:

type car struct {
  brand string
  model string
  doors int
  mileage int
  // wheel is a field containing an anonymous struct
  wheel struct {
    radius int
    material string
  }
}

var myCar = car{
  brand:   "Rezvani",
  model:   "Vengeance",
  doors:   4,
  mileage: 35000,
  wheel: struct {
    radius   int
    material string
  }{
    radius:   35,
    material: "alloy",
  },
}

When Should You Use an Anonymous Struct?

In general, prefer named structs. Named structs make it easier to read and understand your code, and they have the nice side-effect of being reusable. I sometimes use anonymous structs when I know I won't ever need to use a struct again. For example, sometimes I'll use one to create the shape of some JSON data in HTTP handlers.

If a struct is only meant to be used once, then it makes sense to declare it in such a way that developers down the road won't be tempted to accidentally use it again.