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package main
import "fmt"
type Code int
const (
OK Code = 1
BadRequest Code = 2
InvalidParam Code = 3
)
func main() {
fmt.Println(BadRequest)
}
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运行结果：
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$ ls
go.mod go.sum main.go
$ go run .
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Code是int类型，正常情况下，输出是整形数字。
下面看下使用go generate和官方的stringer是什么效果。
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go install golang.org/x/tools/cmd/stringer
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在代码的任意地方添加一行 //go:generate stringer -type=Code
注意，//后面不能有空格
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package main
import "fmt"
//go:generate stringer -type=Code
type Code int
const (
OK Code = 1
BadRequest Code = 2
InvalidParam Code = 3
)
func main() {
fmt.Println(BadRequest)
}
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运行结果：
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$ go generate
$ ls
code_string.go go.mod go.sum main.go
$ go run .
BadRequest
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执行go generate后，会生成一个 code_string.go 的文件，其内容如下：
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// Code generated by "stringer -type=Code"; DO NOT EDIT.
package main
import "strconv"
func _() {
// An "invalid array index" compiler error signifies that the constant values have changed.
// Re-run the stringer command to generate them again.
var x [1]struct{}
_ = x[OK-1]
_ = x[BadRequest-2]
_ = x[InvalidParam-3]
}
const _Code_name = "OKBadRequestInvalidParam"
var _Code_index = [...]uint8{0, 2, 12, 24}
func (i Code) String() string {
i -= 1
if i < 0 || i >= Code(len(_Code_index)-1) {
return "Code(" + strconv.FormatInt(int64(i+1), 10) + ")"
}
return _Code_name[_Code_index[i]:_Code_index[i+1]]
}
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当代码中再次打印 Code 值的时候，输出不再是整形数字，而是变成了字符串，并且是对应的变量名称。
如果再增加一个-linecomment参数，变成//go:generate stringer -type=Code -linecomment，表示打印的时候从注释取值，具体效果如下：
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package main
import "fmt"
//go:generate stringer -type=Code -linecomment
type Code int
const (
OK Code = 1 // 正常OK
BadRequest Code = 2 // 请求错误
InvalidParam Code = 3
)
func main() {
fmt.Println(BadRequest)
fmt.Println(InvalidParam)
}
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执行go generate后生成的 code_string.go 内容如下：
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// Code generated by "stringer -type=Code -linecomment"; DO NOT EDIT.
package main
import "strconv"
func _() {
// An "invalid array index" compiler error signifies that the constant values have changed.
// Re-run the stringer command to generate them again.
var x [1]struct{}
_ = x[OK-1]
_ = x[BadRequest-2]
_ = x[InvalidParam-3]
}
const _Code_name = "正常OK请求错误InvalidParam"
var _Code_index = [...]uint8{0, 8, 20, 32}
func (i Code) String() string {
i -= 1
if i < 0 || i >= Code(len(_Code_index)-1) {
return "Code(" + strconv.FormatInt(int64(i+1), 10) + ")"
}
return _Code_name[_Code_index[i]:_Code_index[i+1]]
}
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运行结果：
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$ go run .
请求错误
InvalidParam
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可见，加了-linecomment参数后，如果变量有注释，则打印内容默认为注释，否则默认为变量名称。
更多参数：
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$ stringer -h
Usage of stringer:
stringer [flags] -type T [directory]
stringer [flags] -type T files... # Must be a single package
For more information, see:
https://pkg.go.dev/golang.org/x/tools/cmd/stringer
Flags:
-linecomment
use line comment text as printed text when present
-output string
output file name; default srcdir/<type>_string.go
-tags string
comma-separated list of build tags to apply
-trimprefix prefix
trim the prefix from the generated constant names
-type string
comma-separated list of type names; must be set
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