Variables and Types in Go

📚 Beginner Level ⏱️ 45 minutes 🔧 Hands-on Examples

Introduction to Go's Type System

Go is a statically typed language with a simple yet powerful type system. Understanding types is fundamental to writing efficient and safe Go programs.

Go's Type Philosophy

  • Static Typing: Types are checked at compile time
  • Type Inference: Compiler can deduce types automatically
  • No Implicit Conversions: Explicit conversions required
  • Zero Values: All variables have a default zero value

Variable Declaration

Method 1: var Keyword

var name string = "Alice"
var age int = 30
var isActive bool = true

// Type inference
var city = "New York"  // string inferred

// Declaration without initialization (zero value)
var count int     // 0
var message string // ""
var done bool    // false

Method 2: Short Declaration (:=)

// Inside functions only
name := "Bob"
age := 25
pi := 3.14159

// Multiple variables
x, y := 10, 20
width, height := getSize()

Constants

const Pi = 3.14159
const MaxUsers = 100
const AppName = "MyApp"

// Typed constants
const typedInt int = 42

// Constant expressions
const (
    KB = 1024
    MB = KB * 1024
    GB = MB * 1024
)

Basic Types

Numeric Types

Type Size Range
int8 8 bits -128 to 127
int16 16 bits -32,768 to 32,767
int32 32 bits -2,147,483,648 to 2,147,483,647
int64 64 bits -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
uint8 (byte) 8 bits 0 to 255
float32 32 bits ±1.18e-38 to ±3.4e38
float64 64 bits ±2.23e-308 to ±1.80e308

Type Conversion

var x int = 42
var y float64 = float64(x)  // Explicit conversion
var z uint = uint(x)

// String conversion
import "strconv"

str := strconv.Itoa(42)          // int to string
num, err := strconv.Atoi("42")  // string to int
flt, err := strconv.ParseFloat("3.14", 64)

Custom Types

// Type definition
type UserID int
type Celsius float64
type Fahrenheit float64

// Using custom types
var uid UserID = 12345
var temp Celsius = 25.5

// Type methods
func (c Celsius) ToFahrenheit() Fahrenheit {
    return Fahrenheit(c*9/5 + 32)
}

Zero Values

var i int        // 0
var f float64   // 0.0
var b bool      // false
var s string    // ""
var p *int      // nil
var a []int     // nil
var m map[string]int  // nil
var ch chan int // nil
var fn func()   // nil
var iface interface{} // nil

Type Aliases

// Type alias (same type)
type ByteSize = int64

// Type definition (new type)
type Duration int64

var size ByteSize = 1024  // Can use as int64
var dur Duration = 1000   // New type, needs conversion

🎯 Practice Exercises

Exercise 1: Temperature Converter

Create custom types for Celsius, Fahrenheit, and Kelvin with conversion methods between them.

Exercise 2: Safe Calculator

Build a calculator that handles division by zero and integer overflow safely.

Exercise 3: Type Detective

Write a function that identifies and prints the type of any variable using reflection.

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