為什麼在 Go 中匯入特定類型時出現「已匯入但未使用」和「未定義」錯誤？

Import Package and Type

Question:

In the following project structure:

src
|-->config
       |--> config.go
|-->otherPackage
       |--> otherFile.go
|-->main.go

There is a type defined in config.go that needs to be used in otherFile.go. However, attempting to import it using the following statement results in errors:

import (
    "fmt"
    "math"
    "../config"
)

The specific errors are:

• Imported and not used.
• Undefined: Config

Even though the type Config is used in a function declaration.

What is the underlying problem?

Answer:

The issue stems from trying to import only a specific type from a package. In Go, it is not possible to import specific elements from a package. When importing a package, you are essentially importing its entire contents.

In this case, since the package where the Config type is defined is named config, importing it will make its types and other identifiers available under the config namespace. For instance, to use Config, it must be referenced as config.Config.

Therefore, to resolve the problem, one of the following solutions can be employed:

• Rename the config variable: Since in otherFile.go there is a variable named config, which shadows the imported package, it should be renamed to avoid conflicts.
• Reference Config using the qualified name: If renaming is not an option, then the type Config can still be used by referencing it with its qualified name, which would be config.Config.

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