Constants

• Constants
• Naming Convention
• Typed Constants
• Untyped Constants
• Enumerated Constants
• Enumeration Expressions

Naming Convention

• all constants are preceded with the const keyword
• naming in camelCase
• value can't be changed
• has to be assignable at compile time
• can be shadowed

  package main 
  
  import ("fmt")
  
  func main () {
      const myConst int = 42
      fmt.Printf("%v, %T", myConst, myConst)
  }
  

Typed Constants

• can be made up any of the primitive types

Untyped Constants

• compiler can infer the type of a constant
• can handle implicit type conversion, if an untyped constant is used in a function
• go const n = 22 var b int16 = 28 n + b // will be of type int16 ```go package main

import ("fmt")

func main () { const myConst = 42 fmt.Printf("%v, %T", myConst, myConst) }

## Enumerated Constants
- first value of `iota` is 0, which may create a false match if some of your logic expects on of the enumerated types to be 0
```go
package main 

import ("fmt")

// const block
const (
    a = iota
    b = iota
    c = iota
)

const (
    a2 = iota
)

func main () {
    fmt.Printf("%v\n", a) // 0
    fmt.Printf("%v\n", b) // 1
    fmt.Printf("%v\n", c) // 2

    // iota scoped to const block
    fmt.Printf("%v\n", a2) // 0

}

- can use _ as variable name, write only variable, for the first value if we don't care for it

Enumeration Expressions

• can define enumeration values dynamically by using either arithmetic, bitwise, or bit-shifting operations

  package main 
  
  import ("fmt")
  
  // const block
  const (
      // can offset values in const block
      a = iota + 5
      b
      c
  )
  
  func main () {
      fmt.Printf("%v\n", a) // 5
      fmt.Printf("%v\n", b) // 6
      fmt.Printf("%v\n", c) // 7
  }
  

  package main 
  
  import ("fmt")
  
  // const block
  const (
      isAdmin = 1 << iota
      isHeadquarters
      canSeeFinancial
  )
  
  func main () {
      var roles byte = isAdmin | canSeeFinancial
      fmt.Printf("%b/n", roles) // 101
  
      // apply bit mask to see if user has permission
      fmt.Printf("Is Admin? %v", isAdmin & roles == isAdmin) // true
  }