[Golang] Enum and String Representation
Recently I use Go enums [2] [4] to represent the type of webpage:
package lib
// Type of the webpage, determined according to path of URL
type PageType int
const (
RootPage PageType = iota
AboutPage
WordPage
NoSuchPage
)
// Determine the type of the webpage according to path of URL.
func DeterminePageType(urlpath string) PageType
// implementation ignored
}
After reading the discussion of reddit, I found that I can use go:generate and stringer command to indirectly get the string representation of enumerated type (i.e., enum name).
First install stringer command:
$ go get -u golang.org/x/tools/cmd/stringer
Give hint to go generate command in the code by adding the comment:
//go:generate stringer -type=PageType
So the code will become:
package lib
// Type of the webpage, determined according to path of URL
//go:generate stringer -type=PageType
type PageType int
const (
RootPage PageType = iota
AboutPage
WordPage
NoSuchPage
)
// Determine the type of the webpage according to path of URL.
func DeterminePageType(urlpath string) PageType
// implementation ignored
}
Run go generate command in the directory of the source code:
$ go generate
A file named pagetype_string.go will be generated automatically. The content of pagetype_string.go is:
// Code generated by "stringer -type=PageType"; DO NOT EDIT.
package lib
import "fmt"
const _PageType_name = "RootPageAboutPageWordPageNoSuchPage"
var _PageType_index = [...]uint8{0, 8, 17, 25, 35}
func (i PageType) String() string {
if i < 0 || i >= PageType(len(_PageType_index)-1) {
return fmt.Sprintf("PageType(%d)", i)
}
return _PageType_name[_PageType_index[i]:_PageType_index[i+1]]
}
An example usage of string representation of enum is to print the enum name if something goes wrong in the testing code:
package lib
import "testing"
func TestDeterminePageType(t *testing.T) {
if pt := DeterminePageType("/"); pt != RootPage {
t.Error("wrong type: ", pt.String())
}
}
Tested on: Go 1.8, Ubuntu Linux 16.10
References:
| [1] |
| [2] |
| [3] |
| [4] | Constants - Effective Go - The Go Programming Language |
| [5] |
| [6] | Generating code - The Go Blog |
| [7] |