cannot refer to unexported name m.β

Question

Have a look at these two simple packages:

package m
const β = 1

package main
import ("m";"fmt")
func main() {
    fmt.Println(m.β)
}

I get this error when I try to compile them:

$ GOPATH=`pwd` go run a.go 
# command-line-arguments
./a.go:4: cannot refer to unexported name m.β
./a.go:4: undefined: m.β

Why? I tried replacing the β with B in both packages, and it works, but I'm trying to use the proper symbol here. Maybe both packages are using homoglyphs or different encodings for some reason?

Answer 1

The go specifications say that an identifier is exported if

the first character of the identifier's name is a Unicode upper case letter (Unicode class "Lu")

https://golang.org/ref/spec#Exported_identifiers

func main() {
    fmt.Println(unicode.IsUpper('β'))
}

returns

false

http://play.golang.org/p/6KxF5-Cq8P

Answer 2

β is lowercase, so it is not exported and can't be used from outside that package.

fmt.Println(unicode.IsLower('β'))

playground

Answer 3

A function , method in an exported package needs to start with an upper case letter. Ran into the same problem yesterday Error in importing custom packages in Go Lang