# 4.8 注释和日志 (Comments and Logging)

### 注释 (Comments)

Comments in Sway start with two slashes and continue until the end of the line. For comments that extend beyond a single line, you'll need to include `//` on each line.

Sway 中的注释以两个斜杠开头，一直持续到行尾。对于超出单行的注释，您需要在每行中包含`//`。

```
// hello world
```

```
// let's make a couple of lines
// commented.

```

You can also place comments at the ends of lines containing code.

您还可以在包含代码的行的末尾放置注释。

```
fn main() {
    let baz = 8; // Eight is a lucky number
}

```

You can also do block comments\
你也可以采用块注释

```
fn main() {
    /*
    You can write on multiple lines
    like this if you want
    */
    let baz = 8;
}

```

### 日志 (Logging)

The `logging` library provides a generic `log` function that can be imported using `use std::logging::log` and used to log variables of any type. Each call to `log` appends a `receipt` to the list of receipts. There are two types of receipts that a `log` can generate: `Log` and `LogData`.

`logging` 库提供了一个通用的 `log` 函数，可以使用 `use std::logging::log` 导入，并日志任何类型的变量。每次调用 `log` 都会在收据列表中附加一个 `receipt`。 `log` 可以生成两种类型的收据：`Log` 和 `LogData`。

```
fn log_values(){
  // Generates a Log receipt
  log(42);

  // Generates a LogData receipt
  let string = "sway";
  log(string);
}

```

#### `日志`收据 (`Log` Receipt)

The `Log` receipt is generated for *non-reference* types, namely `bool`, `u8`, `u16`, `u32`, and `u64`. For example, logging an integer variable `x` that holds the value `42` using `log(x)` may generate the following receipt:

`Log` 收据是为 *non-reference* 类型生成的，即 `bool`、`u8`、`u16`、`u32` 和 `u64`。例如，使用 `log(x)` 记录一个包含值 `42` 的整数变量 `x` 可能会生成以下收据：

```
"Log": {
  "id": "0000000000000000000000000000000000000000000000000000000000000000",
  "is": 10352,
  "pc": 10404,
  "ra": 42,
  "rb": 1018205,
  "rc": 0,
  "rd": 0
}

```

Note that `ra` will include the value being logged. The additional registers `rc` and `rd` will be zero when using `log` while `rb` may include a non-zero value representing a unique ID for the `log` instance. The unique ID is not meaningful on its own but allows the Rust and the TS SDKs to know the type of the data being logged, by looking up the log ID in the JSON ABI file.

请注意，`ra` 将包含记录的值。使用 `log` 时，附加寄存器 `rc` 和 `rd` 将为零，而 `rb` 可能包含一个非零值，表示 `log` 实例的唯一 ID。唯一 ID 本身没有意义，但允许 Rust 和 TS SDK 通过在 JSON ABI 文件中查找日志 ID 来了解正在记录的数据类型。

#### `LogData` 收据 （`LogData` Receipt）

`LogData` is generated for *reference* types which include all types except for the *non\_reference* types mentioned above. For example, logging a `b256` variable `b` that holds the value `0x1111111111111111111111111111111111111111111111111111111111111111` using `log(b)` may generate the following receipt:

`LogData` 是为 *reference* 类型生成的，其中包括除上述 *non\_reference* 之外的所有类型。例如，使用 `log(b)` 记录一个包含值 `0x111111111111111111111111111111111111111111111111111111111111111` 的 `b256` 变量 `b` 可能会生成以下收据：

```
"LogData": {
  "data": "1111111111111111111111111111111111111111111111111111111111111111",
  "digest": "02d449a31fbb267c8f352e9968a79e3e5fc95c1bbeaa502fd6454ebde5a4bedc",
  "id": "0000000000000000000000000000000000000000000000000000000000000000",
  "is": 10352,
  "len": 32,
  "pc": 10444,
  "ptr": 10468,
  "ra": 0,
  "rb": 1018194
}

```

Note that `data` in the receipt above will include the value being logged as a hexadecimal. Similarly to the `Log` receipt, additional registers are written: `ra` will always be zero when using `log`, while `rb` will contain a unique ID for the `log` instance.

请注意，上面收据中的`data 数据`将包含以十六进制形式记录的值。与 `Log` 收据类似，写入额外的寄存器：`ra` 在使用 `log` 时始终为零，而 `rb` 将包含 `log` 实例的唯一 ID。

> **Note** The Rust SDK exposes [APIs](https://fuellabs.github.io/fuels-rs/master/calling-contracts/logs.html#logs) that allow you to retrieve the logged values and display them nicely based on their types as indicated in the JSON ABI file.\
> **注意** Rust SDK 公开了 [API](https://fuelabs.github.io/fuels-rs/master/calling-contracts/logs.html#logs)，允许您检索记录的值，并很好地显示它们—基于 JSON ABI 文件中指示的类型。


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