// Go程序，演示如何检查指针是否为nil
package main
import (
    "fmt"
)
type Temp struct {
}
func main() {
    var pnt *Temp // 指针
    var x = "123"
    var pnt1 *string = &x;
    fmt.Printf("pnt is a nil pointer: %v\n", pnt == nil)
    fmt.Printf("pnt1 is a nil pointer: %v\n", pnt1 == nil)
}

pnt is a nil pointer: true
pnt1 is a nil pointer: false

// Go程序，演示如何检查接口是否为nil
package main
import (
    "fmt"
)

// 创建一个接口
type tank interface {
    Tarea() float64
    Volume() float64
}

type myvalue struct {
    radius float64
    height float64
}

// 实现tank接口的方法
func (m myvalue) Tarea() float64 {

    return 2*m.radius*m.height +
        2*3.14*m.radius*m.radius
}

func (m myvalue) Volume() float64 {

    return 3.14 * m.radius * m.radius * m.height
}

func main() {

    var t tank
    fmt.Printf("t is a nil interface: %v\n", t == nil)

    t = myvalue{10, 14}

    fmt.Printf("t is a nil interface: %v\n", t == nil)

}

t is a nil interface: true
t is a nil interface: false

// Go程序，演示如何检查具有nil指针的接口是否为nil接口
package main
import (
    "fmt"
)
type Temp struct {
}
func main() {

    // 取一个指针
    var val *Temp

    // 取一个接口
    var val2 interface{}

    // val2是一个非nil接口，
    // 持有一个nil指针（val）
    val2 = val

    fmt.Printf("val2 is a nil interface: %v\n", val2 == nil)

    fmt.Printf("val2 is a interface holding a nil pointer: %v\n", val2 == (*Temp)(nil))
}

val2 is a nil interface: false
val2 is a interface holding a nil pointer: true