为什么我的特征数据库指针为零？

Question

var myDB *db.DB

func init() {
    myDB, err := db.OpenDB("db")
    if err := myDB.Create("Feeds"); err != nil {}
    if err := myDB.Create("Votes"); err != nil {}
}

func idb() {
    for _, name := range myDB.AllCols() {
        fmt.Printf("I have a collection called %s
", name)
    }    
}

func main() {
    idb()
}

I get the following error:

runtime error: invalid memory address or nil pointer dereference

It is probably because myDB is nil, but why and how can I fix it so I can setup myDB in init?

Note that if I just drop everything in main without using a global variable, it works.

Answer 1

Short variable declarations

A short variable declaration uses the syntax:

ShortVarDecl = IdentifierList ":=" ExpressionList .

It is shorthand for a regular variable declaration with initializer expressions but no types:

"var" IdentifierList = ExpressionList .

myDB is a local init function variable. := is a short variable declaration.

myDB, err := db.OpenDB("db")

To update package myDB variable, write,

var err error
myDB, err = db.OpenDB("db")