Import Packages
Using external and internal packages in Go programs
📥 What is Importing Packages?
Importing packages in Go allows you to use code from other packages in your program. You can import standard library packages, third-party packages, or your own custom packages.
package main
import (
"fmt" // Standard library
"math/rand" // Standard library
"time" // Standard library
)
func main() {
fmt.Println("Random number:", rand.Intn(100))
}
Output:
Random number: 42
Import Concepts
Single Import
Import one package at a time
import "fmt"Multiple Imports
Import multiple packages together
import (
"fmt"
"time"
)Package Aliases
Give packages custom names
import f "fmt"
f.Println("Hello")Blank Import
Import for side effects only
import _ "database/sql"🔹 Basic Import Syntax
Different ways to import packages in Go:
🔸 Single Package Import:
package main
import "fmt"
func main() {
fmt.Println("Hello, World!")
}🔸 Multiple Package Import:
package main
import (
"fmt"
"math"
"strings"
)
func main() {
fmt.Println("Square root of 16:", math.Sqrt(16))
fmt.Println("Uppercase:", strings.ToUpper("hello"))
}Output:
Square root of 16: 4
Uppercase: HELLO
🔹 Package Aliases
Use aliases to avoid naming conflicts or shorten long package names:
package main
import (
"fmt"
f "fmt" // Alias 'f' for fmt
str "strings" // Alias 'str' for strings
"math/rand"
r "math/rand" // Alias 'r' for rand
)
func main() {
// Using original names
fmt.Println("Original fmt")
// Using aliases
f.Println("Aliased fmt")
result := str.ToUpper("hello")
fmt.Println("Strings result:", result)
number := r.Intn(100)
fmt.Println("Random number:", number)
}Output:
Original fmt
Aliased fmt
Strings result: HELLO
Random number: 73
🔹 Dot Import
Import package contents directly into current namespace:
package main
import (
. "fmt" // Dot import - use functions directly
. "math" // Import math functions directly
)
func main() {
// No need to prefix with package name
Println("Hello from dot import!")
Println("Square root of 25:", Sqrt(25))
Println("Value of Pi:", Pi)
}Output:
Hello from dot import!
Square root of 25: 5
Value of Pi: 3.141592653589793
⚠️ Warning:
Dot imports can make code harder to read and cause naming conflicts. Use sparingly!
🔹 Blank Import
Import packages for their side effects without using them directly:
package main
import (
"fmt"
_ "math/rand" // Blank import for initialization
"time"
)
func init() {
// This runs when the package is imported
fmt.Println("Package initialized")
}
func main() {
fmt.Println("Main function")
fmt.Println("Current time:", time.Now().Format("15:04:05"))
}Output:
Package initialized
Main function
Current time: 14:30:25
🔹 Importing Custom Packages
Import your own packages from the same project:
🔸 Project Structure:
// myproject/
// ├── main.go
// ├── utils/
// │ └── helper.go
// └── models/
// └── user.go
// File: utils/helper.go
package utils
import "strings"
func Capitalize(s string) string {
if len(s) == 0 {
return s
}
return strings.ToUpper(s[:1]) + s[1:]
}
// File: models/user.go
package models
type User struct {
ID int
Name string
}
func NewUser(id int, name string) User {
return User{ID: id, Name: name}
}🔸 File: main.go
package main
import (
"fmt"
"myproject/utils" // Import custom package
"myproject/models" // Import another custom package
)
func main() {
// Use custom packages
name := utils.Capitalize("john doe")
user := models.NewUser(1, name)
fmt.Printf("User: %+v\n", user)
}Output:
User: {ID:1 Name:John doe}