TopolearnStructs are how you model data in Go; there are no classes.
A struct is a typed collection of named fields:
type User struct {
ID int
Name string
Admin bool
}Create values with a composite literal. Prefer naming the fields, User{ID: 1, Name: "Ann"}; omitted fields get their zero values, and the code keeps compiling when fields are added. The positional form User{1, "Ann", false} must list every field in order and breaks when the struct changes.
Access fields with a dot: u.Name. Field visibility follows the package rule — upper-case fields are exported, which also controls whether packages like encoding/json can see them.
Structs are values. Assigning v := u or passing u to a function copies all fields; changing the copy doesn't touch the original. To share and mutate one value, use a pointer (next lesson). Two structs are comparable with == when all their fields are comparable, which also makes them usable as map keys.
Anonymous structs, point := struct{ X, Y int }{1, 2}, are handy for one-off data such as test tables. The empty struct struct{} takes zero bytes and is used for set values and signal-only channels.
A common pattern is a constructor function named NewThing that validates input and returns a ready-to-use value — Go has no constructors built in, so this is a convention, not a language feature.
Example
package main
import "fmt"
type Point struct {
X, Y int
}
type Rect struct {
Min, Max Point
Label string
}
func main() {
r := Rect{Min: Point{0, 0}, Max: Point{4, 3}, Label: "box"}
w := r.Max.X - r.Min.X
fmt.Println(w, r.Label) // 4 box
r2 := r // copies every field
r2.Label = "copy"
fmt.Println(r.Label, r2.Label) // box copy
fmt.Println(Point{1, 2} == Point{1, 2}) // true
fmt.Printf("%+v\n", r.Max) // {X:4 Y:3}
}Remember
- Use keyed literals:
T{Field: v}; missing fields are zero - Assignment copies a struct; use pointers to share
- Structs with comparable fields support == and can be map keys
Watch out for
- Using positional struct literals for types from other packages — they break when fields are added.