1.10 有类型常量和无类型常量的区别？
===================================

在 Go 语言中，常量分为有类型常量和无类型常量。

.. code:: go

   // 有类型常量
   const VERSION string = "v1.0.0"

   // 无类型常量
   const RELEASE = 3

那么他们有什么区别呢？

当你把有无类型的常量，赋值给一个变量的时候，无类型的常量会被隐式的转化成对应的类型

.. code:: go

   package main

   import "fmt"


   func main() {
       const RELEASE = 3

       var x int16 = RELEASE
       var y int32 = RELEASE
       fmt.Printf("type: %T \n", x) //type: int16
       fmt.Printf("type: %T \n", y) //type: int32 
   }

可要是有类型常量，不就会进行转换，在赋值的时候，类型检查就不会通过，从而直接报错

.. code:: go

   package main

   import "fmt"


   func main() {
       const RELEASE int8 = 3

       var x int16 = RELEASE //cannot use RELEASE (type int8) as type int16 in assignment
       var y int32 = RELEASE //cannot use RELEASE (type int8) as type int32 in assignment
       fmt.Printf("type: %T \n", x) 
       fmt.Printf("type: %T \n", y) 
   }

解决的方法是进行显式的转换

.. code:: go

   package main

   import "fmt"


   func main() {
       const RELEASE int8 = 3

       var x int16 = int16(RELEASE) 
       var y int32 = int32(RELEASE) 
       fmt.Printf("type: %T \n", x)  // type: int16
       fmt.Printf("type: %T \n", y)  // type: int32
   }