Go for Return Day1 20230919

Return and handle an error

In greetings/greetings.go, add the code below.

Go 复制代码
package greetings

import (
	"errors"
	"fmt"
)

// Hello returns a greeting for the named person.
func Hello(name string) (string, error) {
	// If no name was given, return an error with a message.
	if name == "" {
		return "", errors.New("empty name")
	}

	// If a name was received, return a value that embeds the name
	// in a greeting message.
	message := fmt.Sprintf("Hi, %v. Welcome!", name)
	return message, nil
}

2.In your hello/hello.go file, handle the error now returned by the Hello function, along with the non-error value.

Go 复制代码
package main

import (
	"fmt"
	"log"

	"example.com/greetings"
)

func main() {
	// Set properties of the predefined Logger, including
	// the log entry prefix and a flag to disable printing
	// the time, source file, and line number.
	log.SetPrefix("greetings: ")
	log.SetFlags(0)

	// Request a greeting message
	message, err := greetings.Hello("")
	// If an error was returned , print it to the console and exit the program.
	if err != nil {
		log.Fatal(err)
	}

	// If no error was returned , print the returned message to the console.
	fmt.Println(message)
}

3.At the command line in the hello directory, run hello.go to confirm that the code works.

Return a random greeting

  • Add a randomFormat function that returns a randomly selected format for a greeting message. Note that randomFormat starts with a lowercase letter, making it accessible only to code in its own package (in other words, it's not exported).
  • In randomFormat, declare a formats slice with three message formats. When declaring a slice, you omit its size in the brackets, like this: []string. This tells Go that the size of the array underlying the slice can be dynamically changed.
  • Use the math/rand package to generate a random number for selecting an item from the slice.
  • In Hello, call the randomFormat function to get a format for the message you'll return, then use the format and name value together to create the message.
  • Return the message (or an error) as you did before.
Go 复制代码
package greetings

import (
	"errors"
	"fmt"
	"math/rand"
)

// Hello returns a greeting for the named person.
func Hello(name string) (string, error) {
	// If no name was given, return an error with a message.
	if name == "" {
		return name, errors.New("empty name")
	}
	// Create a message using a random format.
	message := fmt.Sprintf(randomFormat(), name)
	return message, nil
}

// randomFormat returns one of a set of greeting messages. The returned
// message is selected at random.
func randomFormat() string {
	// A slice of message formats.
	formats := []string{
		"Hi, %v. Welcome!",
		"Great to see you, %v!",
		"Hail, %v! Well met!",
	}

	// Return a randomly selected message format by specifying
	// a random index for the slice of formats.
	return formats[rand.Intn(len(formats))]
}
Go 复制代码
package main

import (
	"fmt"
	"log"

	"example.com/greetings"
)

func main() {
	// Set properties of the predefined Logger, including
	// the log entry prefix and a flag to disable printing
	// the time, source file, and line number.
	log.SetPrefix("greetings: ")
	log.SetFlags(0)

	// Request a greeting message.
	message, err := greetings.Hello("Maxwell")
	// If an error was returned, print it to the console and
	// exit the program.
	if err != nil {
		log.Fatal(err)
	}

	// If no error was returned, print the returned message
	// to the console.
	fmt.Println(message)
}

At the command line, in the hello directory, run hello.go to confirm that the code works. Run it multiple times, noticing that the greeting changes.

Return greetings for multiple people

Go 复制代码
package greetings

import (
	"errors"
	"fmt"
	"math/rand"
)

// Hello returns a greeting for the named person.
func Hello(name string) (string, error) {
	// If no name was given, return an error with a message.
	if name == "" {
		return name, errors.New("empty name")
	}
	// Create a message using a random format.
	message := fmt.Sprintf(randomFormat(), name)
	return message, nil
}

// Hellos returns a map that associates each of the named people
// with a greeting message.
func Hellos(names []string) (map[string]string, error) {
	// A map to associate names with messages.
	messages := make(map[string]string)
	// Loop through the received slice of names, calling
	// the Hello function to get a message for each name.
	for _, name := range names {
		message, err := Hello(name)
		if err != nil {
			return nil, err
		}
		// In the map, associate the retrieved message with
		// the name.
		messages[name] = message
	}
	return messages, nil
}

// randomFormat returns one of a set of greeting messages. The returned
// message is selected at random.
func randomFormat() string {
	// A slice of message formats.
	formats := []string{
		"Hi, %v. Welcome!",
		"Great to see you, %v!",
		"Hail, %v! Well met!",
	}

	// Return a randomly selected message format by specifying
	// a random index for the slice of formats.
	return formats[rand.Intn(len(formats))]
}
Go 复制代码
package main

import (
	"fmt"
	"log"

	"example.com/greetings"
)

func main() {
	// Set properties of the predefined Logger, including
	// the log entry prefix and a flag to disable printing
	// the time, source file, and line number.
	log.SetPrefix("greetings: ")
	log.SetFlags(0)

	// A slice of names.
	names := []string{"Gladys", "Samantha", "Darrin"}

	// Request greeting messages for the names.
	messages, err := greetings.Hellos(names)
	if err != nil {
		log.Fatal(err)
	}
	// If no error was returned, print the returned map of
	// messages to the console.
	fmt.Println(messages)
}
相关推荐
风飘百里4 小时前
分组加密核心原理与实践解析(AES/SM4)
go
岁忧4 小时前
(LeetCode 每日一题) 1865. 找出和为指定值的下标对 (哈希表)
java·c++·算法·leetcode·go·散列表
Wo3Shi4七7 小时前
哈希冲突
数据结构·算法·go
Code季风8 小时前
GORM 部分关键字详解与关联查询实战:Preload 与 Association 的使用对比
go·orm
Code季风8 小时前
深入理解 gRPC 服务定义:从基础到高级
rpc·go
Code季风8 小时前
深入学习 gRPC 流式通信:四种模式详解与实战代码解析
go·grpc
程序员爱钓鱼9 小时前
Go语言泛型-泛型约束与实践
前端·后端·go
程序员爱钓鱼9 小时前
Go语言泛型-泛型对代码结构的优化
后端·google·go
DemonAvenger10 小时前
TCP连接池设计与实现:提升Go应用网络性能
网络协议·架构·go