结构类型不可变

huangapple go评论78阅读模式
英文:

Struct type immtable

问题

我写了一个关于给变量赋值的示例应用程序。请看下面的代码片段:

package main

import (
	"fmt"
)

func main() {
	
	cp := 344
	fmt.Println(cp)
	cp = 566565
	fmt.Println(cp)

	res := []struct {
		Email     string `json:"n.email"`
		Activated bool   `json:"n.activated"`
	}{}

	fmt.Println(res)

	res = []struct {
		Email string `json:"n.email"`
	}{}

	fmt.Println(res)
}

第一个变量 cp,我先赋值,然后再次赋值,它可以正常工作。最后,cp 的值为 566565。对我来说,int 是可变的。

第二段代码不起作用,我尝试将新的结构体重新赋值给 res,但是我得到了编译器错误。

./double_assignment.go:23: cannot use []struct { Email string }
literal (type []struct { Email string }) as type []struct { Email
string; Activated bool } in assignment

结构体是不可变的吗?

英文:

I wrote a sample application about assign value to variable. Look at the following code snippet:

package main

import (
	"fmt"
)

func main() {
	
	cp := 344
	fmt.Println(cp)
	cp = 566565
	fmt.Println(cp)

	res := []struct {
		Email     string `json:"n.email"`
		Activated bool   `json:"n.activated"`
	}{}

	fmt.Println(res)

	res = []struct {
		Email string `json:"n.email"`
	}{}

	fmt.Println(res)
}

First cp variable, I assign value then after do it again and it works. At the end cp carry the value 566565. For me is int mutable.

The second code does not work, reassign new struct to res, I got compiler error.

> ./double_assignment.go:23: cannot use []struct { Email string }
> literal (type []struct { Email string }) as type []struct { Email
> string; Activated bool } in assignment

Is struct immutable?

答案1

得分: 2

第一个短变量声明 res := 设置了一个特定类型 ([]struct { Email string; Activated bool})。

如果你想分配一个不同的类型(在这里,一个不同的 struct 字面量 []struct { Email string }),你需要一个不同的变量。

res2 = []struct {
        Email string `json:"n.email"`
}{}

fmt.Println(res2)

(参考 play.golang.org

英文:

The first short variable declaration res := did set a certain type ([]struct { Email string; Activated bool}).

If you want to assign a different type (here, a different struct literal []struct { Email string }), you need a different variable.

res2 = []struct {
        Email string `json:"n.email"`
}{}

fmt.Println(res2)

(as in play.golang.org )

答案2

得分: 2

不,你的类型不兼容。res 的类型是

[]struct {
    Email     string
    Activated bool
}

但你试图给它一个

[]struct {
    Email string
    // 注意没有 Activated 字段!
}

切片的元素类型是类型的一部分;即使某些字段似乎是共享的,你也不能混合使用。

英文:

No, your types are incompatible. The type of res is

[]struct {
    Email     string
    Activated bool
}

but you are trying to give it a

[]struct {
    Email string
    // notice no Activated!
}

The element type of a slice is part of the type; you can't mix and match like this, even if some fields seem to be shared.

huangapple
  • 本文由 发表于 2014年9月12日 02:39:29
  • 转载请务必保留本文链接:https://go.coder-hub.com/25794794.html
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