Go 中对多个返回值进行转换/类型断言的惯用方法

在 Go 中强制转换多个返回值的惯用方法是什么？

你能在一行中完成吗? 或者你需要使用临时变量，就像我在下面的例子中做的那样？

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")
}
}

顺便问一下，当涉及到接口时，它是否被称为 casting？

i := interface.(int)
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最佳答案

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 cast conversion is different:

var a int
var b int64


a = 5
b = int64(a)
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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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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.

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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.


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