Golang声称我的方法未定义，但它就在那里。

huangapple
go评论105阅读模式
英文:

Golang claims my method is undefined, but it's RIGHT THERE

问题

我很难理解为什么Go无法识别来自其包外部的一个单独方法。这在其他使用包外方法时并没有发生。我对Go还比较新，所以我想知道是否有一些作用域方面的问题我没有注意到。

database.go:

  1. package database
  3. type Database struct {
  4.     fileString    string
  5. }

db-table-person.go:

  1. package database
  3. import (
  4.     "context"
  5. )
  7. type Person struct {
  8.     Name    string
  9.     Age     int
  10. }
  12. func (db *Database) AddPerson(ctx context.Context, person *Person) error {
  13.    // 添加一个人到数据库的代码
  14. }

get-objects-from-file.go:

  1. package myapp
  3. import (
  4.     "encoding/json"
  5.     "os"
  6.     "ioutil"
  7.     
  8.     database "path/to/database/package/that/works/for/every/other/database/method"
  9. )
  11. type BundleOfObjects struct {
  12.     People []database.People
  13.     Dogs   []database.Dogs
  14. }
  16. func LoadObjectsFromFile(filename string) (objects BundleOfObjects) {
  17.     jsonFile, _ := os.Open(filename)
  18.     defer jsonFile.Close()
  20.     bytevalue, _ := ioutil.ReadAll(jsonFile)
  22.     var objects BundleOfObjects
  24.     _ = json.Unmarshal(byteValue, &BundleOfObjects)
  26.     return BundleOfObjects
  27. }

main.go:

  1. package main
  3. import (
  4.     "context"
  6.     database "path/to/database/package/that/works/for/every/other/method/in/the/database/package/"
  7.     myapp "path/to/myapp/that/works/for/every/other/method/in/myapp"
  8. )
  10. func main() {
  11.     filename := "myfile.json"
  13.     bundleOfObjects := myapp.LoadObjectsFromFile(filename)
  15.     for _, p := range bundleOfObjects.People {
  16.         database.AddPerson(context.Background(), p)
  17.     }
  18. }
  19.

我得到了以下错误，指向main.go中对AddPerson的调用：undefined: database.AddPerson。

我再次强调，我已经成功地在这三个包中共享了许多方法，没有任何问题，似乎都使用了完全相同的过程。我漏掉了什么？

英文:

I'm having trouble understanding why Go isn't recognizing one singular method from outside of its package. This isn't happening with any other methods used outside of their packages. I am rather new to Go, so I'm wondering if there is some aspect of scope that I'm just missing.

database.go:

  1. package database
  3. type Database struct {
  4.     fileString    string
  5. }

db-table-person.go:

  1. package database
  3. import (
  4.     "context"
  5. )
  7. type Person struct {
  8.     Name    string
  9.     Age     int
  10. }
  12. func (db *Database) AddPerson(ctx context.Context, person *Person) error {
  13.    // code to add a person to a database
  14. }

get-objects-from-file.go:

  1. package myapp
  3. import (
  4.     "encoding/json"
  5.     "os"
  6.     "ioutil"
  7.     
  8.     database "path/to/database/package/that/works/for/every/other/database/method"
  9. )
  11. type BundleOfObjects struct {
  12.     People []database.People
  13.     Dogs   []database.Dogs
  14. }
  16. func LoadObjectsFromFile(filename string) (objects BundleOfObjects) {
  17.     jsonFile, _ := os.Open(filename)
  18.     defer jsonFile.Close()
  20.     bytevalue, _ := ioutil.ReadAll(jsonFile)
  22.     var objects BundleOfObjects
  24.     _ = json.Unmarshal(byteValue, &BundleOfObjects)
  26.     return BundleOfObjects
  27. }

main.go:

  1. package main
  3. import (
  4.     "context"
  6.     database "path/to/database/package/that/works/for/every/other/method/in/the/database/package/"
  7.     myapp "path/to/myapp/that/works/for/every/other/method/in/myapp"
  8. )
  10. func main() {
  11.     filename := "myfile.json"
  13.     bundleOfObjects := myapp.LoadObjectsFromFile(filename)
  15.     for _, p := range bundleOfObjects.People {
  16.         database.AddPerson(context.Background(), p)
  17.     }
  18. }
  19.

I get the following error referencing the call to AddPerson in main.go: undefined: database.AddPerson

I cannot stress enough that I have successfully shared many methods throughout these three packages with zero issues whatsoever, all seemingly using this exact same process. What am I missing?

答案1

得分: 1

一如既往，在发布问题后的一两分钟内，答案就显而易见了。问题在于AddPerson()是一个方法，而不仅仅是一个没有接收器的函数。它需要在现有的Database实例上调用。因此，在main.go中，我需要首先创建一个数据库实例，然后使用它来调用AddPerson()。像这样：

main.go：

  1. package main
  3. import (
  4.     "context"
  6.     database "path/to/database/package/that/works/for/every/other/method/in/the/database/package/"
  7.     myapp "path/to/myapp/that/works/for/every/other/method/in/myapp"
  8. )
  10. func main() {
  11.     filename := "myfile.json"
  12.     db := database.Database{fileString: "my-database.db"}
  15.     bundleOfObjects := myapp.LoadObjectsFromFile(filename)
  17.     for _, p := range bundleOfObjects.People {
  18.         db.AddPerson(context.Background(), p)
  19.     }
  20. }
英文:

As always, just a minute or two after posting my question, the answer becomes apparent. The problem is that AddPerson() is a method, not just a function without a receiver. It needs to be called on an existing instance of Database. So in main.go, I would need to create a database instance first and then use it to call AddPerson(). Like so:

main.go:

  1. package main
  3. import (
  4.     "context"
  6.     database "path/to/database/package/that/works/for/every/other/method/in/the/database/package/"
  7.     myapp "path/to/myapp/that/works/for/every/other/method/in/myapp"
  8. )
  10. func main() {
  11.     filename := "myfile.json"
  12.     db := database.Database{fileString: "my-database.db"}
  15.     bundleOfObjects := myapp.LoadObjectsFromFile(filename)
  17.     for _, p := range bundleOfObjects.People {
  18.         db.AddPerson(context.Background(), p)
  19.     }
  20. }

huangapple
  • 本文由 发表于 2023年6月21日 04:58:39
  • 转载请务必保留本文链接：https://go.coder-hub.com/76518348.html
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