英文:
Idiomatic way to do conversion/type assertion on multiple return values in Go
问题
在Go语言中，将多个返回值转换为特定类型的惯用方法是使用临时变量。你需要使用一个临时变量来接收多个返回值，然后将其转换为所需的类型。以下是示例代码：
package main
import "fmt"
func oneRet() interface{} {
return "Hello"
}
func twoRet() (interface{}, error) {
return "Hejsan", nil
}
func main() {
// 对于一个返回值，可以直接这样做
str1 := oneRet().(string)
fmt.Println("String 1: " + str1)
// 对于两个返回值，不太容易
//str2, err := twoRet().(string) // 不可行
// 我真的需要使用一个临时变量吗？
temp, err := twoRet()
str2 := temp.(string)
fmt.Println("String 2: " + str2)
if err != nil {
panic("unreachable")
}
}
顺便问一下，当涉及到接口时，这被称为类型断言吗？
i := interface.(int)
英文:
What is the idiomatic way to cast multiple return values in Go?
Can you do it in a single line, or do you need to use temporary variables such as I've done in my example below?
package main
import "fmt"
func oneRet() interface{} {
return "Hello"
}
func twoRet() (interface{}, error) {
return "Hejsan", nil
}
func main() {
// With one return value, you can simply do this
str1 := oneRet().(string)
fmt.Println("String 1: " + str1)
// It is not as easy with two return values
//str2, err := twoRet().(string) // Not possible
// Do I really have to use a temp variable instead?
temp, err := twoRet()
str2 := temp.(string)
fmt.Println("String 2: " + str2 )
if err != nil {
panic("unreachable")
}
}
By the way, is it called casting when it comes to interfaces?
i := interface.(int)
答案1
得分: 73
你不能在一行中完成它。
你的临时变量方法是正确的。
顺便问一下，当涉及到接口时，它被称为转换吗？
实际上，它被称为type assertion。
类型转换是不同的：
var a int
var b int64
a = 5
b = int64(a)
英文:
You can't do it in a single line.
Your temporary variable approach is the way to go.
> By the way, is it called casting when it comes to interfaces?
It is actually called a type assertion.
A type <strike>cast</strike> conversion is different:
var a int
var b int64
a = 5
b = int64(a)
答案2
得分: 44
func silly() (interface{}, error) {
return "愚蠢", nil
}
v, err := silly()
if err != nil {
// 处理错误
}
s, ok := v.(string)
if !ok {
// 断言失败
}
但更有可能的是，你实际上想要使用类型切换，像这样：
switch t := v.(type) {
case string:
// t 是一个字符串
case int:
// t 是一个整数
default:
// t 是我们没有命名的其他类型
}
Go 更关注正确性而不是简洁性。
英文:
func silly() (interface{}, error) {
return "silly", nil
}
v, err := silly()
if err != nil {
// handle error
}
s, ok := v.(string)
if !ok {
// the assertion failed.
}
but more likely what you actually want is to use a type switch, like-a-this:
switch t := v.(type) {
case string:
// t is a string
case int :
// t is an int
default:
// t is some other type that we didn't name.
}
Go is really more about correctness than it is about terseness.
答案3
得分: 30
如果只是一个if语句：
if v, ok := value.(migrater); ok {
v.migrate()
}
Go语言会在if语句中处理类型转换，并允许您访问转换后类型的属性。
英文:
Or just in a single if:
if v, ok := value.(migrater); ok {
v.migrate()
}
Go will take care of the cast inside the if clause and let you access the properties of the casted type.
答案4
得分: 12
template.Must 是标准库中只返回一个语句中的第一个返回值的方法。对于你的情况，可以类似地实现：
func must(v interface{}, err error) interface{} {
if err != nil {
panic(err)
}
return v
}
// 使用方法：
str2 := must(twoRet()).(string)
通过使用 must，你基本上表示不应该出现错误，如果出现错误，程序将无法（或至少不应该）继续运行，而是会引发 panic。
英文:
template.Must is the standard library's approach for returning only the first return value in one statement. Could be done similarly for your case:
func must(v interface{}, err error) interface{} {
if err != nil {
panic(err)
}
return v
}
// Usage:
str2 := must(twoRet()).(string)
By using must you basically say that there should never be an error, and if there is, then the program can't (or at least shouldn't) keep operating, and will panic instead.
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