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137 lines
3.1 KiB
Markdown
137 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=157f51ae0e8cf3ceb45632b537ebe3560a5500b7)
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## 想要更改顯示錯誤的語言
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請為您的語言下載 Erg
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但是，外部庫可能不支持多種語言
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## 只想更改記錄的某些屬性
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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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## 想要隱藏變量
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使用 Erg 無法在相同范圍內進行遮蔽。但是，如果范圍發生變化，您可以重新定義它們(這是一種稱為實例塊的語法)
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````python
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## 獲取一個 T!-type 對象，最后將它作為 T 類型賦值給一個變量
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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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## 想以某種方式重用最終類(不可繼承的類)
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您可以創建一個包裝類。這就是所謂的構圖模式
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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舉類型
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可以定義其他語言中常見的傳統枚舉類型(代數數據類型)如下
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如果您實現"單例"，則類和實例是相同的
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此外，如果您使用 `Enum`，則選擇的類型會自動定義為重定向屬性
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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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# 相當于
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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開頭枚舉
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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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## 想要測試一個(白盒)非公共 API
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`foo.er` 中的私有 API 可在 `foo.test.er` 模塊中特別訪問
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`foo.test.er` 模塊無法導入，因此它保持隱藏狀態
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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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## 想定義一個從外部只讀的(變量)屬性
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您可以將屬性設為私有并定義一個 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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## 希望在類型系統上識別參數名稱
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您可以按記錄接收參數
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```python
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Point = {x = Int; y = Int}
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norm: Point -> Int
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norm({x: Int; y: Int}): Int = x**2 + y**2
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assert norm({x = 1; y = 2}) == norm({y = 2; x = 1})
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```
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## 想要停止警告
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Erg 中沒有停止警告的選項(這是設計使然)。請重寫你的代碼
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