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98 lines
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2.5 KiB
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98 lines
No EOL
2.5 KiB
Markdown
# 闭包
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[](https://gezf7g7pd5.execute-api.ap-northeast-1.amazonaws.com/default/source_up_to_date?owner=erg-lang&repos=erg&ref=main&path=doc/EN/syntax/24_closure.md&commit_hash=e959b3e54bfa8cee4929743b0193a129e7525c61)
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Erg子例程有一个称为"闭包"的功能，可以捕获外部变量
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```python
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outer = 1
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f x = outer + x
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assert f(1) == 2
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```
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与不可变对象一样，可变对象也可以被捕获
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```python
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sum = !0
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for! 1..10, i =>
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sum.add!i
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assert sum == 45
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p!x=
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sum.add!x
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p!(1)
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assert sum == 46
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```
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但是请注意，函数不能捕获可变对象
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如果可以在函数中引用可变对象，则可以编写如下代码
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```python,compile_fail
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# !!! 这段代码实际上给出了一个错误！！！
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i = !0
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f x = i + x
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assert f 1 == 1
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i.add! 1
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assert f 1 == 2
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```
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该函数应该为相同的参数返回相同的值，但假设被打破了
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请注意，`i`仅在调用时进行评估
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如果您想在定义函数时获取可变对象的内容，请调用`.clone`
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```python
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i = !0
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immut_i = i.clone().freeze()
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fx = immut_i + x
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assert f 1 == 1
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i.add! 1
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assert f 1 == 1
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```
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## avoid mutable state, functional programming
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```python
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# Erg
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sum = !0
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for! 1..10, i =>
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sum.add!i
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assert sum == 45
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```
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上面的等效程序可以用Python编写如下:
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```python,checker_ignore
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# Python
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sum = 0
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for i in range(1, 10):
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sum += i
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assert sum == 45
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```
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但是，Erg 建议使用更简单的表示法
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与其使用子例程和可变对象来传递状态，不如使用一种使用函数来定位状态的风格。这称为函数式编程
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```python
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# 功能风格
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sum = (1..10).sum()
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assert sum == 45
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```
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上面的代码给出了与之前完全相同的结果，但是您可以看到这个代码要简单得多
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`fold`函数可以用来做比sum更多的事情
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`fold`是一个迭代器方法，它为每次迭代执行参数`f`
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累加结果的计数器的初始值在`init`中指定，并在`acc`中累加
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```python
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# 从0开始，结果会
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sum = (1..10).fold(init: 0, f: (acc, i) -> acc + i)
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assert sum == 45
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```
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Erg被设计为对使用不可变对象进行编程的自然简洁描述
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<p align='center'>
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<a href='./23_subroutine.md'>上一页</a> | <a href='./25_module.md'>下一页</a>
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</p> |