11种编程语言中，返回多个不同类型的方法样例
本文分享自华为云社区《多语言编程 返回多个不同类型的方法样例》，作者： 张俭 。背景
你可能会在一些场景下碰到需要返回多个不同类型的方法。比如协议解析读取报文时，更具体地像kubernetes在开始解析Yaml的时候，怎么知道这个类型是属于Deployment还是Service？
C
C语言通常通过使用Struct（结构体）和Union（联合体）的方式来实现这个功能，如下文例子
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef enum {
MONKEY,
COW,
UNKNOWN
} AnimalType;
typedef struct {
char* description;
} Monkey;
typedef struct {
char* description;
} Cow;
typedef struct {
AnimalType type;
union {
Monkey monkey;
Cow cow;
};
} Animal;
Animal createAnimal(const char* animalType) {
Animal animal;
if (strcmp(animalType, "Monkey") == 0) {
animal.type = MONKEY;
animal.monkey.description = "I am a monkey!";
} else if (strcmp(animalType, "Cow") == 0) {
animal.type = COW;
animal.cow.description = "I am a cow!";
} else {
animal.type = UNKNOWN;
}
return animal;
}
int main() {
Animal animal1 = createAnimal("Monkey");
if (animal1.type == MONKEY) {
printf("%s\n", animal1.monkey.description);
}
Animal animal2 = createAnimal("Cow");
if (animal2.type == COW) {
printf("%s\n", animal2.cow.description);
}
Animal animal3 = createAnimal("Dog");
if (animal3.type == UNKNOWN) {
printf("Unknown animal type\n");
}
return 0;
}C++
在C++中，我们可以使用基类指针来指向派生类的对象。可以使用动态类型识别（RTTI）来在运行时确定对象的类型
#include <iostream>
#include <stdexcept>
class Animal {
public:
virtual std::string toString() const = 0;
};
class Monkey : public Animal {
public:
std::string toString() const override {
return "I am a monkey!";
}
};
class Cow : public Animal {
public:
std::string toString() const override {
return "I am a cow!";
}
};
Animal* createAnimal(const std::string& animalType) {
if (animalType == "Monkey") {
return new Monkey();
}
if (animalType == "Cow") {
return new Cow();
}
throw std::runtime_error("Unknown animal type: " + animalType);
}
int main() {
try {
Animal* animal1 = createAnimal("Monkey");
if (Monkey* monkey = dynamic_cast<Monkey*>(animal1)) {
std::cout << monkey->toString() << std::endl;
}
delete animal1;
Animal* animal2 = createAnimal("Cow");
if (Cow* cow = dynamic_cast<Cow*>(animal2)) {
std::cout << cow->toString() << std::endl;
}
delete animal2;
}
catch (const std::runtime_error& e) {
std::cerr << e.what() << std::endl;
}
return 0;
}使用SealedClass
package main
import (
"fmt"
)
type Animal interface {
String() string
}
type Monkey struct{}
func (m Monkey) String() string {
return "I am a monkey!"
}
type Cow struct{}
func (c Cow) String() string {
return "I am a cow!"
}
func createAnimal(typeName string) (Animal, error) {
switch typeName {
case "Monkey":
return Monkey{}, nil
case "Cow":
return Cow{}, nil
default:
return nil, fmt.Errorf("Unknown animal type: %s", typeName)
}
}
func main() {
animal1, err := createAnimal("Monkey")
if err != nil {
fmt.Println(err)
return
}
if monkey, ok := animal1.(Monkey); ok {
fmt.Println(monkey)
}
animal2, err := createAnimal("Cow")
if err != nil {
fmt.Println(err)
return
}
if cow, ok := animal2.(Cow); ok {
fmt.Println(cow)
}
}Python
Python是动态类型的语言，可以简单基于一些条件返回不同类型的对象，然后在接收到返回值之后使用type()函数或isinstance()函数来确定其类型
public class MultiTypeReturnExample {
static class Monkey {
@Override
public String toString() {
return "I am a monkey!";
}
}
static class Cow {
@Override
public String toString() {
return "I am a cow!";
}
}
public static Object createAnimal(String type) throws IllegalArgumentException {
switch (type) {
case "Monkey":
return new Monkey();
case "Cow":
return new Cow();
default:
throw new IllegalArgumentException("Unknown animal type: " + type);
}
}
public static void main(String[] args) throws Exception {
Object animal1 = createAnimal("Monkey");
// java8 写法，后面如果明确用做精确的类型，需要强制转换
if (animal1 instanceof Monkey) {
System.out.println(animal1);
}
Object animal2 = createAnimal("Cow");
if (animal2 instanceof Cow) {
System.out.println(animal2);
}
// java17 写法，不需要强制转换
if (createAnimal("Monkey") instanceof Monkey animal3) {
System.out.println(animal3);
}
if (createAnimal("Cow") instanceof Cow animal4) {
System.out.println(animal4);
}
}
}Ruby
Ruby也较为简单，在方法内部直接返回不同类型的对象。然后，可以使用is_a方法或class方法来确定返回对象的实际类型。
class Animal {
toString() {
return 'I am an animal';
}
}
class Monkey extends Animal {
toString() {
return 'I am a monkey';
}
}
class Cow extends Animal {
toString() {
return 'I am a cow';
}
}
function createAnimal(animalType) {
switch (animalType) {
case 'Monkey':
return new Monkey();
case 'Cow':
return new Cow();
default:
throw new Error(`Unknown animal type: ${animalType}`);
}
}
try {
const animal1 = createAnimal('Monkey');
if (animal1 instanceof Monkey) {
console.log(animal1.toString());
}
const animal2 = createAnimal('Cow');
if (animal2 instanceof Cow) {
console.log(animal2.toString());
}
const animal3 = createAnimal('Dog');
} catch (error) {
console.error(error.message);
}Rust
在Rust中，可以使用enum（枚举）来创建一个持有多种不同类型的数据结构。然后使用match语句来做模式匹配。
use std::fmt;enum Animal { Monkey, Cow,}impl fmt::Display for Animal { fn fmt(&self, f: &mut fmt::Formatter
页:
[1]