If I want to scan through a string, I can do this:
~~~go
package main
import (
"fmt"
"strings"
)
func main() {
r := strings.NewReader("west north east")
for {
var s string
_, e := fmt.Fscan(r, &s)
fmt.Printf("%q %v\n", s, e)
if e != nil { break }
}
}
~~~
Result:
~~~
"west" <nil>
"north" <nil>
"east" <nil>
"" EOF
~~~
I recently discovered `fmt.Scanner` [1], so I thought I would try to
implement it. I came up with this:
~~~go
package main
import (
"fmt"
"strings"
)
type comma struct { tok string }
func (c *comma) Scan(s fmt.ScanState, r rune) error {
tok, err := s.Token(false, func(r rune) bool {
return r != ','
})
if err != nil {
return err
}
c.tok = string(tok)
if _, _, err := s.ReadRune(); err != nil {
return err
}
return nil
}
func main() {
r := strings.NewReader("west,north,east")
for {
var c comma
_, e := fmt.Fscan(r, &c)
fmt.Printf("%q %v\n", c.tok, e)
if e != nil { break }
}
}
~~~
Result:
~~~
"west" <nil>
"north" <nil>
"east" unexpected EOF
~~~
So the result is pretty similar, but what bothers me is the `unexpected
EOF`. It seems it is due to this code:
https://github.com/golang/go/blob/3075ffc93e962792ddf43b2a528ef19b1577ffb7/src/fmt/scan.go#L956-L966
It seems like `EOF` should be valid in this case, or perhaps I dont
understand the reasoning for it to be unexpected.
1. https://golang.org/pkg/fmt#Scanner
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