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193 lines
No EOL
4.3 KiB
Markdown
# 可见性
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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/20_visibility.md&commit_hash=e959b3e54bfa8cee4929743b0193a129e7525c61)
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Erg 变量具有 __visibility__ 的概念
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到目前为止，我们看到的所有变量都称为 __private variables__。这是一个外部不可见的变量
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例如，`foo` 模块中定义的私有变量不能被另一个模块引用
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```python
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# foo.er
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x = "this is an invisible variable"
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```
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```python,compile_fail
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# bar.er
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foo = import "foo"
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foo.x # AttributeError: 模块 'foo' 没有属性 'x' ('x' 是私有的)
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```
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另一方面，也有__public variables__，可以从外部引用
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公共变量用`.`定义
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```python
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# foo.er
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.x = "this is a visible variable"
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```
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```python
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# bar.er
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foo = import "foo"
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assert foo.x == "this is a visible variable"
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```
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您不需要向私有变量添加任何内容，但您也可以添加 `::` 或 `self::`(用于类型等的`Self::`)以表明它们是私有的。增加。如果它是一个模块，它也可以是 `module::`
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```python
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::x = "this is an invisible variable"
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assert ::x == x
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assert self ::x == ::x
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assert module::x == ::x
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```
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In the context of purely sequential execution, private variables are almost synonymous with local variables. It can be referenced from the inner scope.
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```python
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::x = "this is a private variable"
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y =
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x + 1 # 完全是 module::x
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```
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通过使用`::`，可以区分作用域内同名的变量
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在左侧指定要引用的变量的范围。为顶层指定 `module`
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如果未指定，则照常引用最里面的变量
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```python
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::x = 0
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assert x == 0
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y =
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::x = 1
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assert x == 1
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z =
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::x = 2
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assert ::x == 2
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assert z::x == 2
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assert y::x == 1
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assert module::x == 0
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```
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在匿名子程序作用域中，`self` 指定了它自己的作用域
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```python
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x = 0
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f = x ->
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log module::x, self::x
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f1# 0 1
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```
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`::` 还负责访问私有实例属性
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```python
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x = 0
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C = Class {x = Int}
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C.
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# 顶级 x 被引用(警告使用 module::x)
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f1 self = x
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# 实例属性 x 被引用
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f2 self = self::x
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```
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## 外部模块中的可见性
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在一个模块中定义的类实际上可以定义来自外部模块的方法
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```python,compile_fail
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# foo.er
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.Foo = Class()
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```
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```python
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# bar.er
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{Foo;} = import "foo"
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Foo::
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private self = pass
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Foo.
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public self = self::private()
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.f() =
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foo = Foo.new()
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foo.public()
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foo::private() # 属性错误
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```
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但是，这两种方法都只在该模块中可用
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外部定义的私有方法对 Foo 类的方法仅在定义模块内可见
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公共方法暴露在类之外，但不在模块之外
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```python
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# baz.er
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{Foo;} = import "foo"
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foo = Foo.new()
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foo.public() # 属性错误: "Foo"没有属性"public"("public"在模块"bar"中定义)
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```
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此外，方法不能在要重新导出的类型中定义
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这是为了避免混淆方法是否找到，具体取决于导入方法的模块
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```python,compile_fail
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# bar.er
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{.Foo;} = import "foo"
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.Foo::
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private self = pass # 错误
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Foo.
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public self = self::private() # 错误
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```
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如果你想做这样的事情，定义一个 [patch](./type/07_patch.md)
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```python
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# bar.er
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{Foo;} = import "foo"
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FooImpl = Patch Foo
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FooImpl :=:
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private self = pass
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Foo Impl.
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public self = self::private()
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```
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```python
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# baz.er
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{Foo;} = import "foo"
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{FooImpl;} = import "bar"
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foo = Foo.new()
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foo.public()
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```
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## 受限公共变量
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可变可见性不限于完全公共/私有
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您也可以有限制地发布
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```python,checker_ignore
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# foo.er
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.record = {
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.a = {
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.(.record)x = 0
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.(module)y = 0
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.z = 0
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}
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_ = .a.x # OK
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_ = .a.y # OK
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_ = .a.z # OK
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}
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_ = .record.a.x # 可见性错误
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_ = .record.a.y # OK
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_ = .record.a.z # OK
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```
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```python,checker_ignore
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foo = import "foo"
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_ = foo.record.a.x # 可见性错误
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_ = foo.record.a.y # 可见性错误
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_ = foo.record.a.z # OK
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```
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<p align='center'>
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