Command-Line Programs

Validation Errors

A command can validate input and report a message instead of exiting the process.

validation Validation checks whether a value is acceptable before the program uses it.

Validation Errors

count
validation_errors.go
Replay: real traced execution (multi-file project)
package main

import "fmt"

func validateCount(count int) string {
	if count < 1 {
		return "count must be at least 1"
	}
	if count > 5 {
		return "count must be 5 or less"
	}
	return "ok"
}

func main() {
	var count = 3
	message := validateCount(count)
	allowed := message == "ok"

	fmt.Println("count=", count)
	fmt.Println("allowed=", allowed)
	fmt.Println("message=", message)
}

package main

import "fmt"

func validateCount(count int) string {
	if count < 1 {
		return "count must be at least 1"
	}
	if count > 5 {
		return "count must be 5 or less"
	}
	return "ok"
}

func main() {
	var count = 0
	message := validateCount(count)
	allowed := message == "ok"

	fmt.Println("count=", count)
	fmt.Println("allowed=", allowed)
	fmt.Println("message=", message)
}

package main

import "fmt"

func validateCount(count int) string {
	if count < 1 {
		return "count must be at least 1"
	}
	if count > 5 {
		return "count must be 5 or less"
	}
	return "ok"
}

func main() {
	var count = 8
	message := validateCount(count)
	allowed := message == "ok"

	fmt.Println("count=", count)
	fmt.Println("allowed=", allowed)
	fmt.Println("message=", message)
}

  1. count ← 3

    15func main() {16  var count→ 3 = 3 //@count=0, 817  message := validateCount(count3)18  allowed := message == "ok"

  2. func validateCount(count int) string

    5func validateCount(count3 int) string {6  if count < 1 {7    return "count must be at least 1"8  }9  if count > 5 {10    return "count must be 5 or less"11  }12  return "ok"13}

  3. message ← "ok", allowed ← true

    16  var count = 3 //@count=0, 817  message→ "ok" := validateCount(count3)18  allowed→ true := message"ok" == "ok"1920  fmt.Println("count=", count3)21  fmt.Println("allowed=", allowedtrue)22  fmt.Println("message=", message"ok")23}
    outputcount= 3
allowed= true
message= ok

  1. count ← 0

    15func main() {16  var count→ 0 = 017  message := validateCount(count0)18  allowed := message == "ok"

  2. func validateCount(count int) string

    5func validateCount(count0 int) string {6  if count < 1 {

  3. if count < 1

    5func validateCount(count int) string {6  if count0 < 1 {7    return "count must be at least 1"8  }

  4. message ← "count must be at least 1", allowed ← false

    16  var count = 017  message→ "count must be at least 1" := validateCount(count0)18  allowed→ false := message"count must be at least 1" == "ok"1920  fmt.Println("count=", count0)21  fmt.Println("allowed=", allowedfalse)22  fmt.Println("message=", message"count must be at least 1")23}
    outputcount= 0
allowed= false
message= count must be at least 1

  1. count ← 8

    15func main() {16  var count→ 8 = 817  message := validateCount(count8)18  allowed := message == "ok"

  2. func validateCount(count int) string

    5func validateCount(count8 int) string {6  if count < 1 {

  3. if count > 5

    8}9if count8 > 5 {10  return "count must be 5 or less"11}

  4. message ← "count must be 5 or less", allowed ← false

    16  var count = 817  message→ "count must be 5 or less" := validateCount(count8)18  allowed→ false := message"count must be 5 or less" == "ok"1920  fmt.Println("count=", count8)21  fmt.Println("allowed=", allowedfalse)22  fmt.Println("message=", message"count must be 5 or less")23}
    outputcount= 8
allowed= false
message= count must be 5 or less