golang 为什么比较两个指向结构的变量表现不同？

Question

我创建了两个相同结构的实例，当我比较两个指向结构实例的变量时，对输出感到困惑。

package main

import "fmt"

type Person struct {
    name string
}

func main() {
   p1 := &Person{name: "guru"}
   p2 := &Person{name: "guru"}
   fmt.Println(p1 == p2) // false, compares by address?
   p3 := Person{name: "guru"}
   p4 := Person{name: "guru"}
   fmt.Println(p3 == p4) // true , why? compares by content?
}

== 运算符是否像重载运算符一样工作？

Answer 1

p1 == p2是指针比较，比较指针值（内存地址）。由于您使用了 2 个复合文字（并获取了它们的地址），它们将指向 2 个不同的变量，因此地址将不同（因为 Person 的大小不为零）。 Spec: Composite literals:

Taking the address of a composite literal generates a pointer to a unique variable initialized with the literal's value.

p3 == p4 比较结构值，它比较它们 field-by-field，并且由于匹配字段具有相等的值，比较将导致 true.

比较规则在Spec: Comparison operators:

The equality operators == and != apply to operands that are comparable. The ordering operators <, <=, >, and >= apply to operands that are ordered. These terms and the result of the comparisons are defined as follows:

[...]

Pointer values are comparable. Two pointer values are equal if they point to the same variable or if both have value nil. Pointers to distinct zero-size variables may or may not be equal.

[...]

Struct values are comparable if all their fields are comparable. Two struct values are equal if their corresponding non-blank fields are equal.

Answer 2

两个指针值只有在内存中指向相同的值或者在Golang中为nil时才相等。您创建了两个结构实例，因此它们具有不同的地址

   p1 := &Person{name: "guru"}
   p2 := &Person{name: "guru"}

Answer 3

你的第一个例子

p1 := &Person{name: "guru"}
p2 := &Person{name: "guru"}

fmt.Println(p1 == p2) // false, compares by address?

比较两个指针是否相等。由于它们各自寻址不同的内存地址，所以不比较相等。

你的第二个例子，

 p3 := Person{name: "guru"}
 p4 := Person{name: "guru"}

fmt.Println(p3 == p4) // true , why? compares by content?

比较两个结构并按值进行比较，因此它们比较相等。

如果您在比较之前取消引用 指针，您会发现它们比较相等。例如，给定

p1 := &Person{ name: "guru" }
p2 := &Person{ name: "guru" }
p3 :=  Person{ name: "guru" }
p4 :=  Person{ name: "guru" }

以下所有比较相等：

*p1 == *p2
*p1 == p3
p3 == *p2
p3 == p4

golang 为什么比较两个指向结构的变量表现不同？

golang why comparing two variables pointing to struct behaves differently?

go

pointers

struct

comparison