How to Parse a List of Values as a Flag in Golang?

Acquiring a List of Values as a Flag in Golang

In Golang, the standard flag package provides the ability to parse flags from the command line, but it inherently supports only primitive types such as strings, integers, and booleans. To handle a list of values as a flag, one can implement a custom flag.Value type and utilize flag.Var() for binding it.

An example implementation is available below:

import (
    "flag"
    "fmt"
)

type arrayFlags []string

// String is a required implementation of the flag.Value interface
func (i *arrayFlags) String() string {
    return fmt.Sprintf("%v", *i)
}

// Set is another required implementation of the flag.Value interface
func (i *arrayFlags) Set(value string) error {
    *i = append(*i, value)
    return nil
}

var myFlags arrayFlags

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

This custom flag type can then be used to pass multiple flag values, such as:

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

In summary, by implementing a custom flag.Value type and utilizing flag.Var(), Golang allows developers to parse a list of values as flags, providing greater flexibility in command-line argument handling.

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