args is a generic library for optional arguments. It is inspired by Dave Cheney's functional options idea. It can also serve the purpose of Python "kwargs" for Go programs.
Optional arguments are defined using New and its typed variants.
These arguments are basically functions that return argument values
of type args.V. To use these argument values, your function receives
a variadic list of args.V and then gets the value of each argument:
var Port = args.NewInt()
var RoundTripper = args.New(Default(http.DefaultTransport))
var Timeout = args.NewDuration(Flag("timeout", 10*time.Second, "timeout"))
func MyServer(args ...args.V) {
port := Port.Get(args)
rt := RoundTripper.Get(args)
to := Timeout.Get(args)
...
}
MyServer()
MyServer(Timeout(1 * time.Second))
MyServer(Timeout(2 * time.Second), RoundTripper(MyTransport))args can load default values from flags as well as user-defined
constants.
To use user-defined types instead of the generic args.V,
you need to write a few lines of boiler-plates:
var roundTripper = args.New(http.DefaultTransport)
var timeout = args.NewDuration()
type ServerOpt args.V
func RoundTripper(r http.RoundTripper) ServerOpt { return ServerOpt(roundTripper(r)) }
func Timeout(d time.Duration) ServerOpt { return ServerOpt(d) }
func MyServer(opts ...ServerOpt) {
rt := roundTripper.Get(opts).(http.RoundTripper)
to := timeout.Get(opts)
...
}Note that, args is focused on easy-to-use APIs. It is not efficient and is wasteful if the function is frequently invoked.