Implementing an interface in Go - go

Question

My project is organized as follows
github.com/achanda/poke
├── cmd
│   └── poke.go
├── scanner.go
├── txt_scanner.go
└── types.go
The files are as follows
# cat scanner.go
package poke
type Scanner interface {
Scan() *ScanResult
}
# cat txt_scanner.go
package poke
type txtScanner struct {
txt string
}
func newTxtScanner(host string) Scanner {
return txtScanner{txt}
}
func (tcpcs txtScanner) Scan() *ScanResult {
// do stuff
return &result
}
Now I am trying to call this in my main package (in poke.go) like this
package main
import "github.com/achanda/poke"
func main() {
var sr poke.Scanner
sr = poke.txtScanner{txt}
sr.Scan()
}
This fails to run with
# command-line-arguments
./poke.go:111: cannot refer to unexported name poke.txtScanner
./poke.go:111: undefined: portscan.txtScanner
What am I doing wrong?

Answer 1

you need to access type or field outside package, so you should export them using first letter upper case:
first you should define your txtScanner and txt string with first upper case letter, otherwise you will see this error too:
.\poke.go:8: implicit assignment of unexported field 'txt' in poke.TxtScanner literal
like this:
type TxtScanner struct {
Txt string
}
also see newTxtScanner(host string) function in this working sample codes:
poke.go:
package main
import "github.com/achanda/poke"
func main() {
s := "test"
var sr poke.Scanner
sr = poke.TxtScanner{s}
sr.Scan()
}
txt_scanner.go:
package poke
type TxtScanner struct {
Txt string
}
func newTxtScanner(host string) Scanner {
return TxtScanner{host}
}
func (tcpcs TxtScanner) Scan() *ScanResult {
// do stuff
result := ScanResult{}
return &result
}
types.go:
package poke
type ScanResult struct {
}
scanner.go:
package poke
type Scanner interface {
Scan() *ScanResult
}