// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// These examples demonstrate more intricate uses of the flag package.
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package flag_test
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import (
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"errors"
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"flag"
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"fmt"
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"strings"
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"time"
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)
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// Example 1: A single string flag called "species" with default value "gopher".
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var species = flag.String("species", "gopher", "the species we are studying")
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// Example 2: Two flags sharing a variable, so we can have a shorthand.
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// The order of initialization is undefined, so make sure both use the
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// same default value. They must be set up with an init function.
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var gopherType string
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func init() {
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const (
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defaultGopher = "pocket"
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usage = "the variety of gopher"
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)
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flag.StringVar(&gopherType, "gopher_type", defaultGopher, usage)
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flag.StringVar(&gopherType, "g", defaultGopher, usage+" (shorthand)")
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}
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// Example 3: A user-defined flag type, a slice of durations.
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type interval []time.Duration
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// String is the method to format the flag's value, part of the flag.Value interface.
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// The String method's output will be used in diagnostics.
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func (i *interval) String() string {
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return fmt.Sprint(*i)
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}
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// Set is the method to set the flag value, part of the flag.Value interface.
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// Set's argument is a string to be parsed to set the flag.
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// It's a comma-separated list, so we split it.
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func (i *interval) Set(value string) error {
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// If we wanted to allow the flag to be set multiple times,
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// accumulating values, we would delete this if statement.
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// That would permit usages such as
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// -deltaT 10s -deltaT 15s
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// and other combinations.
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if len(*i) > 0 {
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return errors.New("interval flag already set")
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}
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for _, dt := range strings.Split(value, ",") {
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duration, err := time.ParseDuration(dt)
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if err != nil {
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return err
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}
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*i = append(*i, duration)
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}
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return nil
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}
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// Define a flag to accumulate durations. Because it has a special type,
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// we need to use the Var function and therefore create the flag during
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// init.
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var intervalFlag interval
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func init() {
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// Tie the command-line flag to the intervalFlag variable and
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// set a usage message.
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flag.Var(&intervalFlag, "deltaT", "comma-separated list of intervals to use between events")
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}
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func Example() {
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// All the interesting pieces are with the variables declared above, but
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// to enable the flag package to see the flags defined there, one must
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// execute, typically at the start of main (not init!):
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// flag.Parse()
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// We don't run it here because this is not a main function and
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// the testing suite has already parsed the flags.
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}
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