example_func_test.go

Documentation: flag

		 1  // Copyright 2020 The Go Authors. All rights reserved.
		 2  // Use of this source code is governed by a BSD-style
		 3  // license that can be found in the LICENSE file.
		 4  
		 5  package flag_test
		 6  
		 7  import (
		 8  	"errors"
		 9  	"flag"
		10  	"fmt"
		11  	"net"
		12  	"os"
		13  )
		14  
		15  func ExampleFunc() {
		16  	fs := flag.NewFlagSet("ExampleFunc", flag.ContinueOnError)
		17  	fs.SetOutput(os.Stdout)
		18  	var ip net.IP
		19  	fs.Func("ip", "`IP address` to parse", func(s string) error {
		20  		ip = net.ParseIP(s)
		21  		if ip == nil {
		22  			return errors.New("could not parse IP")
		23  		}
		24  		return nil
		25  	})
		26  	fs.Parse([]string{"-ip", "127.0.0.1"})
		27  	fmt.Printf("{ip: %v, loopback: %t}\n\n", ip, ip.IsLoopback())
		28  
		29  	// 256 is not a valid IPv4 component
		30  	fs.Parse([]string{"-ip", "256.0.0.1"})
		31  	fmt.Printf("{ip: %v, loopback: %t}\n\n", ip, ip.IsLoopback())
		32  
		33  	// Output:
		34  	// {ip: 127.0.0.1, loopback: true}
		35  	//
		36  	// invalid value "256.0.0.1" for flag -ip: could not parse IP
		37  	// Usage of ExampleFunc:
		38  	//	 -ip IP address
		39  	//		 	IP address to parse
		40  	// {ip: <nil>, loopback: false}
		41  }
		42
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