模拟枚举类型

go语言中虽然没有Java, C++等一些高级语言提供的枚举类型特性,但可以使用常量和iota来模拟。 例如:

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// BuildResult 构建结果
type BuildResult int

const (
	// Success 成功
	Success BuildResult = iota
	// Fail 失败
	Fail
	// Abort 中断
	Abort
)
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var buildResult = Success
println(buildResult) // 0

使用go generate和stringer生成String() string函数

为了打印枚举类型值具体的字符串标识,可以使用https://godoc.org/golang.org/x/tools/cmd/stringer工具并结合go generate为枚举类型生成func (t T) String() string函数。这样枚举类型就实现了fmt.Stringer接口。具体的实现方式是在枚举类型BuildResult的定义上加上注释//go:generate stringer -type=BuildResult

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// BuildResult 构建结果
//go:generate stringer -type=BuildResult
type BuildResult int

const (
	// Success 成功
	Success BuildResult = iota
	// Fail 失败
	Fail
	// Abort 中断
	Abort
)

在生成代码前需要先按照stringer命令行工具go get -u golang.org/x/tools/cmd/stringer,并将命令执行的$GOPATH/bin配置到$PATH环境变量下。

使用go generate生成代码后,会生成源码buildresult_string.go:

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// Code generated by "stringer -type=BuildResult"; DO NOT EDIT.

package enums

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[Success-0]
	_ = x[Fail-1]
	_ = x[Abort-2]
}

const _BuildResult_name = "SuccessFailAbort"

var _BuildResult_index = [...]uint8{0, 7, 11, 16}

func (i BuildResult) String() string {
	if i < 0 || i >= BuildResult(len(_BuildResult_index)-1) {
		return "BuildResult(" + strconv.FormatInt(int64(i), 10) + ")"
	}
	return _BuildResult_name[_BuildResult_index[i]:_BuildResult_index[i+1]]
}

使用生成的源码:

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var buildResult = Success
println(buildResult.String()) // Success