one important detail i have not found in the other answers is
that stat is declared to return a fs.FileInfo, but printf takes
an empty interface argument and therefor unwraps the interface
value. so if you want to print the actual variable type of interface
variables you can pass a pointer (same is often used with reflection):
// prints "type of &fileinfo = *fs.FileInfo"
fmt.Printf("type of &fileinfo = %T\n", &fileinfo)
On 3/6/22 20:46, jlfo...@berkeley.edu wrote:
(go version go1.17.7 linux/amd64)
Consider the following trivial program:
------
package main
import (
"fmt"
"os"
)
func main() {
file := "."
fileinfo, _ := os.Stat(file)
fmt.Printf("type of fileinfo = %T\n", fileinfo)
}
------
This runs and produces the output
type of fileinfo = *os.fileStat
Fine, but notice that "fileStat" isn't capitalized. This means this
symbol isn't
exported outside the "os" package. Yet, somehow the "fileinfo" variable
is assigned
this type.
Indeed, if I try to explicitly use the "os.fileStat" type in the
program, the program fails to compile, e.g.
------------
package main
import (
"fmt"
"os"
)
func main() {
var fileinfo *os.fileStat
file := "."
fileinfo, _ = os.Stat(file)
fmt.Printf("type of fileinfo = %T\n", fileinfo)
}
-----
results in
./x3.go:9:16: cannot refer to unexported name os.fileStat
./x3.go:12:14: cannot assign fs.FileInfo to fileinfo (type *os.fileStat)
in multiple assignment: need type assertion
./x3.go:12:14: cannot use fs.FileInfo value as type *os.fileStat in
assignment: need type assertion
Notice the first error message.
I also don't understand why the other two error message are produced
when all I did was to explicitly declare a variable that was previously
assigned a value in a short declaration.
What am I missing?
Cordially,
Jon Forrest
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