Structs

# Why Structs Matter

Structs are Go's primary way to model domain data. They keep related fields together, improve type safety, and make APIs self-documenting.

In production systems, clean struct design directly improves validation, serialization, and long-term maintainability.

# Defining and Initializing Structs

Struct zero values are useful by default: each field gets its own zero value. Named-field literals are preferred for readability and safer refactors.

type Person struct {
    Name string
    Age  int
}

p1 := Person{Name: "Alice", Age: 30}
p2 := &Person{Name: "Bob", Age: 25}
var p3 Person

# Embedding for Composition

Embedding promotes fields and methods from the embedded type. It is composition, not inheritance.

type Animal struct{ Name string }
func (a Animal) Speak() string { return a.Name + " speaks" }

type Dog struct {
    Animal
    Breed string
}

d := Dog{Animal: Animal{Name: "Rex"}, Breed: "Lab"}
fmt.Println(d.Name)
fmt.Println(d.Speak())

# Struct Tags and Serialization

Tags add metadata consumed by reflection-based packages like JSON encoders and validators.

type User struct {
    ID       int    `json:"id"`
    Username string `json:"username"`
    Password string `json:"-"`
}

# Practice Challenge

Define a Rectangle struct and implementArea and Perimeter. Bonus: add methods with pointer/value receiver rationale.

package main

import "fmt"

type Rectangle struct {
    Width  float64
    Height float64
}

func Area(r Rectangle) float64 {
    // TODO
}

func Perimeter(r Rectangle) float64 {
    // TODO
}

func main() {
    r := Rectangle{Width: 4, Height: 3}
    fmt.Println("Area:", Area(r))
    fmt.Println("Perimeter:", Perimeter(r))
}