直接看代码

package test

import (
    "fmt"
    "testing"
)

type StructA struct {
    str string
}

func NewStructA() *StructA {
    return nil
}

type InterfaceA interface{}

func ToInterfaceA() InterfaceA {
    return NewStructA() //  NewStructA return nil
}
func ReturnInterface() InterfaceA {
    return nil
}

func TestXXX(t *testing.T) {
    a := ReturnInterface()
    fmt.Println(a == nil)           // true
    fmt.Printf("type of a %T\n", a) // type of a <nil>

    b := NewStructA()
    fmt.Println(b == nil)           // true
    fmt.Printf("type of b %T\n", b) // type of b *test.StructA

    c := ToInterfaceA()
    fmt.Println(c == nil)           // false
    fmt.Printf("type of c %T\n", c) // type of c *test.StructA
}

为什么 c == nil 是false?