友元函数（Friends）

The friend syntax is used to declare modules that are trusted by the current module. A trusted module is allowed to call any function defined in the current module that have the public(friend) visibility. For details on function visibilities, please refer to the Visibility section in Functions.

友元语法用于声明当前模块信任的其它模块。受信任的模块可以调用当前模块中定义的任何具有公开（友元）可见性的函数。有关函数可见性的详细信息，请参阅函数中的可见性部分。

友元声明（Friend declaration）

A module can declare other modules as friends via friend declaration statements, in the format of

一个模块可以通过友元声明语句将其他模块声明为友元，格式为：

friend <address::name> — friend declaration using fully qualified module name like the example below, or
friend <address::name>— 使用完全合格的模块名称的友元声明，如下例所示，或
```
address 0x42 {
module a {
    friend 0x42::b;
}
}
```
friend <module-name-alias> — friend declaration using a module name alias, where the module alias is introduced via the use statement.
friend <module-name-alias>— 使用模块名称别名的友元声明，其中模块别名是通过use语句引入的。
```
address 0x42 {
module a {
   use 0x42::b;
   friend b;
}
}
```

A module may have multiple friend declarations, and the union of all the friend modules forms the friend list. In the example below, both 0x42::B and 0x42::C are considered as friends of 0x42::A.

一个模块可能有多个友元声明，所有好友模块的并集形成友元列表。在下面的示例中，0x42::B和0x42::C都被视为的友元函数0x42::A。

 address 0x42 {
 module a {
     friend 0x42::b;
     friend 0x42::c;
 }
 }

Unlike use statements, friend can only be declared in the module scope and not in the expression block scope. friend declarations may be located anywhere a top-level construct (e.g., use, function, struct, etc.) is allowed. However, for readability, it is advised to place friend declarations near the beginning of the module definition.

与use语句不同，friend只能在模块作用域内声明，而不能在表达式块的作用域内声明。friend声明可以位于允许顶层构造的任何位置（例如， use， function，struct等）是被允许的。但是，为了可读性，建议将友元声明放在模块定义的开头附近。

Note that the concept of friendship does not apply to Move scripts:

A Move script cannot declare friend modules as doing so is considered meaningless: there is no mechanism to call the function defined in a script.
A Move module cannot declare friend scripts as well because scripts are ephemeral code snippets that are never published to global storage.

请注意，友元关系（friendship）的概念不适用于 Move 脚本：

Move 脚本不能声明friend模块，因为这样做被认为是无意义的：没有机制可以调用脚本中定义的函数。
Move 模块也不能声明friend脚本，因为脚本是永远不会发布到全局存储的临时代码片段。

友元声明规则（Friend declaration rules）

Friend declarations are subject to the following rules: 友元声明须遵守以下规则：

A module cannot declare itself as a friend

一个模块不能将自己声明为友元。

address 0x42 {
module m { friend Self; // 错误! }
//                ^^^^ 不能将自己声明为友元
}

address 0x43 {
module m { friend 0x43::M; // 错误! }
//                ^^^^^^^ 不能将自己声明为友元
}

Friend modules must be known by the compiler

编译器必须知道友元模块

address 0x42 {
module m { friend 0x42::nonexistent; // 错误! }
//                ^^^^^^^^^^^^^^^^^ 未绑定的模块 '0x42::nonexistent'
}

Friend modules must be within the same account address. (Note: this is not a technical requirement but rather a policy decision which may be relaxed later.)

友元模块必须在同一个账号地址内。（注：这不是技术要求，而是以后可能放宽的决策。)

address 0x42 {
module m {}
}

address 0x43 {
module n { friend 0x42::m; // 错误! }
//                ^^^^^^^ 不能声明当前地址外的模块作为友元
}

友元关系不能创建循环模块依赖关系（Friends relationships cannot create cyclic module dependencies）

Cycles are not allowed in the friend relationships, e.g., the relation 0x2::a friends 0x2::b friends 0x2::c friends 0x2::a is not allowed. More generally, declaring a friend module adds a dependency upon the current module to the friend module (because the purpose is for the friend to call functions in the current module). If that friend module is already used, either directly or transitively, a cycle of dependencies would be created.

友元关系中不允许循环，例如 0x2::a 友元 0x2::b 友元 0x2::c 友元0x2::a是不允许的。更普遍地，声明一个友元模块会将对当前模块的依赖添加到友元模块（因为目的是让友元调用当前模块中的函数）。如果该友元模块已被直接或传递地使用，则将形成一个依赖循环。

address 0x2 {
module a {
   use 0x2::c;
   friend 0x2::b;

   public fun a() {
       c::c()
   }
}

module b {
   friend 0x2::c; // 错误!
//         ^^^^^^ 这个友元关系形成了一个依赖循环:  '0x2::a' 使用了 '0x2::c' 但'0x2::b' 同时是 '0x2::a'和'0x2::b' 的友元
}

module c {
   public fun c() {}
}
}

The friend list for a module cannot contain duplicates.
模块的友元列表不能包含重复项。

address 0x42 {
module a {}

module m {
   use 0x42::a as aliased_a;
   friend 0x42::A;
   friend aliased_a; // 错误!
//         ^^^^^^^^^ 重复的友元声明 '0x42::a'. 模块内的友元声明必须是唯一的
}
}

Move Book 中文版

友元函数（Friends）

友元声明（Friend declaration）

友元声明规则（Friend declaration rules）