How do you use type assertion to access specific information from an *os.PathError in Go?

Understanding err.(*os.PathError) in Go

While exploring the Go documentation on effective errors, you encountered the line "err.(*os.PathError)" and wondered what it meant.

What is err.(*os.PathError)?

The os.Create function returns an error as its second return value, implementing the error interface { Error() string }. When you attempt to create a file with os.Create, it returns an error if it encounters an issue.

Specifically, if you attempt to create a file when there is no space left on the device, the os package returns an *os.PathError as the error implementation. To access additional information about the error beyond the Error() method, you need to convert it.

Type Assertion

The statement "e, ok := err.(os.PathError)" performs a type assertion. It checks if the interface value err contains a os.PathError as its concrete type. If it does, it assigns the os.PathError to e and sets ok to true. Otherwise, it assigns the zero value of os.PathError (which is nil) to e and sets ok to false.

Usage

In your provided code, you are looking for the ENOSPC error code, which indicates that there is no space left on the device. If the error returned by os.Create matches this code, you can execute a cleanup task to free up some space and then attempt to create the file again.

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