Validating Options

Related Projects ArgumentParser
1

I'm looking to have a filePath option that I can reuse.

The option would validate that filePath exists and is readable, writeable accessible etc..

ExpressibleByArgument doesn't support validate nor transform.
That would be useful.

Ex.
struct FilePath: ExpressibleByArgument {
var pathString: String

init?(argument: String) {
    self.pathString = argument
}

func validate() throws {
    if (FileManager.default.fileExists(atPath: self.pathString)) {
        throw CliError.InvalidFilePath
    }
}

}

2

Definitely seems like a valid request — could you open an issue on the GH repo describing your use case?

3

General per-type validation customization notwithstanding, I wouldn't recommend validating file existence separately from the place where you actually read it. It is very much possible that the file was added/removed between the validation and the actual reading.

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4

The temporal distance between validating access to the filepath in the option verses reading it in the command impl is inconsequential in the majority of cases. If you don't provide a validate method there still is no reason you cannot choose to validate in the command impl itself. This way you have different design options to consider. I think that is a plus.

5

I mean, you do you. The precise requirement most likely differs from case to case.

IME, you still need to re-validate that the file exists when opening it though since that's how most IO frameworks operate. That's why I suggest to just do it during IO operations. You could, of course, assert that IO operations always succeed, but I personally feel that that's not using the framework to its fullest.

1 Like