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@@ -1,2 +1,126 @@
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-# 自定义包中的错误处理和 panicking
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+# 13.4 自定义包中的错误处理和 panicking
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+这是所有自定义包实现者应该遵守的最佳实践：
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+
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+1）*在包内部，总是应该从 panic 中 recover*：不允许显式的超出包范围的 panic()
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+
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+2）*向包的调用者返回错误值（而不是 panic）。*
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+
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+在包内部，特别是在非导出函数中有很深层次的嵌套调用时，对主调函数来说用 panic 来表示应该被翻译成错误的错误场景是很有用的（并且提高了代码可读性）。
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+
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+这在下面的代码中被很好地阐述了。我们有一个简单的 parse 包（示例 13.4）用来把输入的字符串解析为整数切片；这个包有自己特殊的 `ParseError`。
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+
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+当没有东西需要转换或者转换成整数失败时，这个包会 panic（在函数 fields2numbers 中）。但是可导出的 Parse 函数会从 panic 中 recover 并用所有这些信息返回一个错误给调用者。为了演示这个过程，在 panic_recover.go 中 调用了 parse 包（示例 13.4）；不可解析的字符串会导致错误并被打印出来。
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+
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+示例 13.4 [parse.go](examples/chapter_13/parse/parse.go)：
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+
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+```go
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+// parse.go
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+package parse
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+
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+import (
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+ "fmt"
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+ "strings"
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+ "strconv"
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+)
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+
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+// A ParseError indicates an error in converting a word into an integer.
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+type ParseError struct {
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+ Index int // The index into the space-separated list of words.
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+ Word string // The word that generated the parse error.
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+ Err error // The raw error that precipitated this error, if any.
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+}
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+
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+// String returns a human-readable error message.
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+func (e *ParseError) String() string {
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+ return fmt.Sprintf("pkg parse: error parsing %q as int", e.Word)
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+}
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+
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+// Parse parses the space-separated words in in put as integers.
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+func Parse(input string) (numbers []int, err error) {
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+ defer func() {
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+ if r := recover(); r != nil {
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+ var ok bool
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+ err, ok = r.(error)
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+ if !ok {
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+ err = fmt.Errorf("pkg: %v", r)
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+ }
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+ }
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+ }()
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+
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+ fields := strings.Fields(input)
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+ numbers = fields2numbers(fields)
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+ return
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+}
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+
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+func fields2numbers(fields []string) (numbers []int) {
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+ if len(fields) == 0 {
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+ panic("no words to parse")
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+ }
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+ for idx, field := range fields {
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+ num, err := strconv.Atoi(field)
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+ if err != nil {
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+ panic(&ParseError{idx, field, err})
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+ }
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+ numbers = append(numbers, num)
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+ }
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+ return
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+}
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+
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+```
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+
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+示例 13.5 [panic_package.go](examples/chapter_13/panic_package.go)：
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+
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+```go
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+// panic_package.go
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+package main
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+
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+import (
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+ "fmt"
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+ "./parse/parse"
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+)
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+
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+func main() {
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+ var examples = []string{
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+ "1 2 3 4 5",
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+ "100 50 25 12.5 6.25",
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+ "2 + 2 = 4",
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+ "1st class",
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+ "",
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+ }
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+
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+ for _, ex := range examples {
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+ fmt.Printf("Parsing %q:\n ", ex)
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+ nums, err := parse.Parse(ex)
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+ if err != nil {
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+ fmt.Println(err) // here String() method from ParseError is used
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+ continue
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+ }
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+ fmt.Println(nums)
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+ }
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+}
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+
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+```
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+
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+输出：
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+
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+```
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+Parsing "1 2 3 4 5":
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+ [1 2 3 4 5]
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+Parsing "100 50 25 12.5 6.25":
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+ pkg parse: error parsing "12.5" as int
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+Parsing "2 + 2 = 4":
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+ pkg parse: error parsing "+" as int
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+Parsing "1st class":
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+ pkg parse: error parsing "1st" as int
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+Parsing "":
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+ pkg: no words to parse
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+
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+```
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+
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+
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+## 链接
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+
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+- [目录](directory.md)
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+- 上一节：[从 panic 中恢复 （Recover）](13.3.md)
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+- 下一节：[一种用闭包处理错误的模式](13.5.md)
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dake