How to Create Custom Flag Types to Handle List Arguments in Golang?

How to Define Custom Flag Types to Handle List Arguments in Golang

Python's argparse module offers the nargs argument to specify the number of values to be parsed when dealing with lists. Golang's flag package, while supporting basic types, does not provide a direct way to accept lists. Here's how to define your own flag type to address this issue:

Creating a Custom Array Flag Type:

Golang programs can create their own flag types by implementing the flag.Value interface. The following code defines a arrayFlags type to handle arrays of strings:

type arrayFlags []string

// String implements the flag.Value interface to convert the flag value to a string
func (i *arrayFlags) String() string {
    return fmt.Sprintf("%v", *i)
}

// Set implements the flag.Value interface to update the flag value when a new argument is provided
func (i *arrayFlags) Set(value string) error {
    *i = append(*i, value)
    return nil
}

Utilizing the Custom Flag Type:

To use the custom array flag type, you can use the flag.Var() function. Here's an example:

var myFlags arrayFlags

func main() {
    flag.Var(&myFlags, "list1", "Some description for this param.")
    flag.Parse()
}

Parsing Multiple Flags:

You can pass multiple flags like this:

go run your_file.go --list1 value1 --list1 value2

The myFlags variable will now contain the values passed to the list1 flag, providing you with access to the list of values.

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