tagflag

Overview ¶

Package tagflag uses reflection to derive flags and positional arguments to a program, and parses and sets them from a slice of arguments.

For example:

var opts struct {
    Mmap           bool           `help:"memory-map torrent data"`
    TestPeer       []*net.TCPAddr `help:"addresses of some starting peers"`
    tagflag.StartPos              // Marks beginning of positional arguments.
    Torrent        []string       `arity:"+" help:"torrent file path or magnet uri"`
}
tagflag.Parse(&opts)

Supported tags include:

help: a line of text to show after the option
arity: defaults to 1. the number of arguments a field requires, or ? for one
       optional argument, + for one or more, or * for zero or more.

MarshalArgs is called on fields that implement ArgsMarshaler. A number of arguments matching the arity of the field are passed if possible.

Slices will collect successive values, within the provided arity constraints.

A few helpful types have builtin marshallers, for example Bytes, *net.TCPAddr, *url.URL, time.Duration, and net.IP.

Flags are strictly passed with the form -K or -K=V. No space between -K and the value is allowed. This allows positional arguments to be mixed in with flags, and prevents any confusion due to some flags occasionally not taking values. A `--` will terminate flag parsing, and treat all further arguments as positional.

A builtin help and usage printer are provided, and activated when passing -h or -help.

Flag and positional argument names are automatically munged to fit the standard scheme within tagflag.