erg/doc/zh_CN/syntax/28_spread_syntax.md

# 传播赋值

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在分解赋值中，将 `...` 放在变量前面会将所有剩余元素展开到该变量中。 这称为扩展赋值。

```python
[x,...y] = [1, 2, 3]
assert x == 1
assert y == [2, 3]
x, ...y = (1, 2, 3)
assert x == 1
assert y == (2, 3)
```

## 提取赋值

如果在 `...` 之后没有写入任何内容，则忽略并分配剩余的元素。 这种类型的扩展赋值具体称为抽取赋值。
提取分配是一种方便的语法，用于本地化模块或记录中的特定属性。

```python
{sin; cos; tan; ..} = import "math"
```

After that, you can use `sin, cos, tan` locally.

You can do the same with records.

```python
record = {x = 1; y = 2}
{x; y; ...} = record
```

If you want to expand all, use `{*} = record`. It is `open` in OCaml.

```python
record = {x = 1; y = 2}
{*} = records
assert x == 1 and y == 2
```

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