Where can we use Variable Scoping and Shadowing in Go?

Question

Some related posts I found:

• go to variable area and shading
• Golang: scope variable inside if statements
• Limit variable storage

There are also many uses for the Scope and Shadowing variables.
Any code samples or answers will be appreciated.

Answer 1

Variable Visibility and Shading:

Go has a lexical area using blocks:

• The scope of the predefined identifier is the universe block.
• , , , ( ), ( ) .
• package - , .
• , , - .
• , ConstSpec VarSpec (ShortVarDecl ) .
• , TypeSpec .
  , , .
  , , .

; . - , .

:

• ,

---

Go:

• Golang ( ):

  package main
  import "fmt"
  func main() {
      i := 10 //scope: main
      j := 4
      for i := 'a'; i < 'b'; i++ {
          // i shadowed inside this block
          fmt.Println(i, j) //97 4
      }
      fmt.Println(i, j) //10 4
  
      if i := "test"; len(i) == j {
          // i shadowed inside this block
          fmt.Println(i, j) // i= test , j= 4
      } else {
          // i shadowed inside this block
          fmt.Println(i, j) //test 40
      }
      fmt.Println(i, j) //10 4
  }
  

• " ", .
  , :

  { }:
  : , , , ,...

  package main
  import "fmt"
  func main() {
      i := 1
      j := 2
      //new scope :
      {
          i := "hi" //new local var
          j++
          fmt.Println(i, j) //hi 3
      }
      fmt.Println(i, j) //1 3
  }
  

• :
  : , ,
  : / :

  package main
  import "fmt"
  func fun(i int, j *int) {
      i++                //+nice: use as local var without side effect
      *j++               //+nice: intentionally use as global var
      fmt.Println(i, *j) //11 21
  }
  func main() {
      i := 10 //scope: main
      j := 20
      fun(i, &j)
      fmt.Println(i, j) //10 21
  }
  

• :

  package main
  import "fmt"
  var i int = 1 //global
  func main() {
      j := 2
      fmt.Println(i, j) //1 2
      i := 10           //Shadowing global var
      fmt.Println(i, j) //10 2
      fun(i, j)         //10 2
  }
  func fun(i, j int) {
      //i := 100        //error: no new variables on left side of :=
      //var i int = 100 //error: i redeclared in this block
      fmt.Println(i, j) //10 2
  }
  

: Scope > .
: :