Bool should be able to be set false.

[hfern]

If you have a bool option that defaults to true, there is no way of disabling it from the command line.

You should be able to do this by ./somecommand --boolflag=0

Right now running this results in: "bool flag boolflag cannot have an argument"

[GeertJohan]

When I need a bool that defaults to true, I inverted the meaning/name for the flag and still default to false.

For instance, at one point enabling TLS in a piece of software was optional:
EnableTLS bool long:"enable-tls" At a certain point I decided to make it enabled by default, and so the flag was inverted: `DisableTLS bool `long:"disable-tls"

This way, the bool always defaults to false and command line arguments are more descriptive (imo):
someCommand --disable-tls
versus
someCommand --enable-tls=0

[jessevdk]

I agree with GeertJohan here. bool flags are equivalent to flags without arguments in getopt, which simply turn things on. Apart from inverting the meaning of the flag, you can also just create your own boolean derived type which allows for what you want (if you really want to insist):

type Bool bool

func (b *Bool) UnmarshalFlag(value string) error {
    if value == "true" {
        *b = true
    } else if value == "false" {
        *b = false
    } else {
        return fmt.Errorf("only `true' and `false' are valid values, not `%s'", value)
    }

    return nil
}

func (b Bool) MarshalFlag() string {
    if b {
        return "true"
    }

    return "false"
}

[dmitshur]

When I need a bool that defaults to true, I inverted the meaning/name for the flag and still default to false.

I agree that's a better practice.

In that case, shouldn't go-flags detect it as an error (at init time) and refuse to work? A user of this package should not be able apply default:"true" to a bool flag if it renders the flag completely unfit for its purpose (i.e., able to have more than 1 different value).