Variables declaration in go

• Declaratoin

  var (
      name string
      age int
      city string
  )
      
  -- 
  var (
      name, city string
      age int
  )
      
  -- 
  var name string
  var city string
  var age int
      
  

• Initialization

  var (
      name string = "Chari"
      city string = "BLR"
      mobile int = 12345
  )
  -- Inferred typing
  var (
      name = "Chari"
      city = "BLR"
      mobile = 12345
  )
  --
  var (
      name, city, mobile = "Chari", "BLR", 12345
  )
  

• Short assignment “:=” (Inside a function only)

  func main() {
      name := "Chari"
      city := "BLR"
  }
  

• Function type

  var (
      a = func() {
          fmt.Println("a's function defination")
      }
  )
      
  func main() {
      a()
  }
  -- Output --
  a's function defination
      
  -- another e.g.
  func main() {
      a := func() {
          fmt.Println("a's function defination inside main function")
      }
  }
  

Constants

• define constants

  const (
      name = "Chari"
      fact = true
      Pi = 3.14
  )
      
  --
  const Pi = 3.14
  const fact = false
  

Exported Variables

• Name thats strts with capital is exported; Meaning it can be reffered from other packages.

  -- Below names Pi, ABC, Abc can be used in other packages.
  const Pi = 3.14
  var ABC string = "Foo string"
  var Abc string = "Abc"
      
  -- Below names name, city can not be accessed by other packages, but with in same package.
  var name string = "Chari"
  var city = "BLR"
  
  

Pointers

• declaration

  httpClient := &http.Client{}
  resp, err := httpClient.Get("http://github.com")
      
  Note: You can directly call methods, fileds on pointer without using *
  

• pass by value

  type Counter struct {
      count int
  }
      
  func increase(cnt Counter) int {
      cnt.counter++
      return cnt.counter
  }
      
  func main() {
      c := Counter{count:10}
          
      fmt.Println(increase(c))
          
      fmt.Println(c.count)
  }
      
  -- Output --
  11
  10
  

• pass by reference

  type Counter struct {
      count int
  }
      
  func increase(cnt *Counter) int {
      cnt.count++
      return cnt.count
  }
      
  func main() {
      c := &Counter{count :10}
      fmt.Println(increase(c))
      fmt.Println(c.count)
  }
  -- Output --
  11
  11
      
  -- Other way pass by reference to above program
  -- rewriting only main function
  func main() {
      c := Counter{count:10}
      // & to reffer it's pointer
      fmt.Println(increase(&c))
      fmt.Println(c.count)
  }