Explore unaddressable values ​​in Go

In the Go language, some values ​​are not addressable, that is, their memory addresses cannot be obtained. These values ​​include constants, literals, and expressions that cannot be addressed. In this article, we will explore these non-addressable values ​​and understand their characteristics through concrete code examples.

First, let’s look at some examples of constants. In the Go language, constants are not addressable because their values ​​are determined at compile time and there is no runtime memory address for access. The following is a sample code:

package main

import "fmt"

func main() {
    const x = 10
    fmt.Printf("常量x的地址是：%p
", &x)
}

The above code will cause an error when compiling, prompting that the address of the constant x is not addressable. This is because constants are directly replaced by their values ​​at compile time and cannot be addressed.

In addition to constants, literals are also not addressable. Literals refer to values, strings, etc. written directly in the code. Their values ​​are also determined at compile time and cannot be taken from the address. The following is an example about literals:

package main

import "fmt"

func main() {
    fmt.Printf("字面量1的地址是：%p
", &1)
}

Compiling the above code will result in an error indicating that the address of literal 1 is not addressable. Because 1 is a literal, it is directly replaced by its value at compile time and cannot be accessed by address.

In addition to constants and literals, some expressions are also not addressable. For example, it is illegal to take the address of the return value of a function or to take the address of an unaddressable expression. The following is a sample code:

package main

import "fmt"

func getValue() int {
    return 10
}

func main() {
    val := getValue()
    fmt.Printf("函数返回值的地址是：%p
", &val)
}

In the above code, trying to get the address of the return value of the function getValue() will cause a compilation error because the return value of the function is a temporary and non-addressable value. .

In summary, in Go language, constants, literals and some expressions are not addressable. Taking addresses from these unaddressable values ​​will result in compilation errors. Therefore, you need to pay attention to these characteristics when writing code to avoid unnecessary errors.

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