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139 lines
3.1 KiB
Markdown
139 lines
3.1 KiB
Markdown
# 提示
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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/tips.md&commit_hash=8badf02f399b279a012b54d056b443c6b104a6dd)
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## 想要更改显示错误的语言
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请为您的语言下载 Erg
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但是，外部库可能不支持多种语言
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## 只想更改记录的某些属性
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```python
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record: {.name = Str; .age = Nat; .height = CentiMeter}
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{height; ...rest} = record
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mut_record = {.height = !height; ...rest}
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```
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## 想要隐藏变量
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使用 Erg 无法在相同范围内进行遮蔽。但是，如果范围发生变化，您可以重新定义它们(这是一种称为实例块的语法)
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````python
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## 获取一个 T!-type 对象，最后将它作为 T 类型赋值给一个变量
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x: T =
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x: T! = foo()
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x.bar!()
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x.freeze()
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````
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## 想以某种方式重用最终类(不可继承的类)
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您可以创建一个包装类。这就是所谓的构图模式
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```python
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FinalWrapper = Class {inner = FinalClass}
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FinalWrapper.
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method self =
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self::inner.method()
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...
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```
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## 想使用不是字符串的枚举类型
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可以定义其他语言中常见的传统枚举类型(代数数据类型)如下
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如果您实现"单例"，则类和实例是相同的
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此外，如果您使用 `Enum`，则选择的类型会自动定义为重定向属性
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```python
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Ok = Class Impl := Singleton
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Err = Class Impl := Singleton
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ErrWithInfo = Inherit {info = Str}
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Status = Enum Ok, Err, ErrWithInfo
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stat: Status = Status.new ErrWithInfo.new {info = "error caused by ..."}
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match! stat:
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Status.Ok -> ...
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Status.Err -> ...
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Status.ErrWithInfo::{info} -> ...
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```
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```python
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Status = Enum Ok, Err, ErrWithInfo
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# 相当于
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Status = Class Ok or Err or ErrWithInfo
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Status.
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Ok = Ok
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Err = Err
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ErrWithInfo = ErrWithInfo
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```
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## 我想在1开头枚举
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方法一:
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```python
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arr = [...]
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for! arr.iter().enumerate(start := 1), i =>
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...
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```
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method 2:
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```python
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arr = [...]
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for! arr.iter().zip(1...) , i =>
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...
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```
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## 想要测试一个(白盒)非公共 API
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`foo.er` 中的私有 API 可在 `foo.test.er` 模块中特别访问
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`foo.test.er` 模块无法导入，因此它保持隐藏状态
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```python
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# foo.er
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private x = ...
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```
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```python
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# foo.test.er
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foo = import "foo"
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@Test
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'testing private' x =
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...
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y = foo::private x
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...
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```
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## 在实现特征的方法时，会对未使用的变量发出警告
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您可以将属性设为私有并定义一个 getter
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```python
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C = Class {v = Int!}
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C::
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inc_v!(ref! self) = self::v.inc!()
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...
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C.
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get_v(ref self): Int = self::v.freeze()
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...
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```
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## 希望在类型系统上识别参数名称
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你可以使用`discard`
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```python
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T = Trait {.f = (Self, x: Int, s: Str) -> Int}
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C = Class T
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C|<: T|.
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f self, x, s =
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discard s
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...
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```
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## 想要停止警告
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Erg 中没有停止警告的选项(这是设计使然)。请重写你的代码
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