_internal的语义是什么？ [英] What are the semantics of _internal?

问题描述

在以下示例中，我不断看到对_internal的引用：

I keep seeing references to _internal in examples like the following:

class Symbol {
    final String name;
    static Map<String, Symbol> _cache;

    factory Symbol(String name) {
        if (_cache == null) {
        _cache = {};
     }

     if (_cache.containsKey(name)) {
        return _cache[name];
     } else {
        final symbol = new Symbol._internal(name);
        _cache[name] = symbol;
        return symbol;
      }
    }

  Symbol._internal(this.name);
}

我从代码中收集到它是一个私有的构造函数。最后一行 Symbol._internal（this.name）; 似乎有点令人困惑，因为它似乎是类主体中的语句，而不是方法主体中的语句，这导致我相信这实际上是没有方法主体的内部构造函数定义。

I've gathered from the code that it's a privately accessible constructor. The last line Symbol._internal(this.name); seems a bit confusing because it appears to be a statement within the class body and not within a method body, leading me to believe it's actually the internal constructor definition without a method body.

我的假设正确吗？

推荐答案

_internal 构造只是一个经常为该类私有的构造函数的名称（不需要为 ._ internal 。使用任何 Class._someName 结构创建私有构造函数。）

The _internal construction is just a name often given to constructors that are private to the class (the name is not required to be ._internal you can create a private constructor using any Class._someName construction).

例如，以下代码仅允许您使用缓存构造函数从类外部创建新人员。 ：

For example the following code only allows you to create new persons from outside the class using a caching constructor:

class Person {

    final String name;
    static Map<String,Person> _cache;

    factory Person(String name) {
        if(_cache === null) {
            _cache = new Map<String,Person>();
         }
         if(_cache[name] === null]) {
            _cache[name] = new Person._internal(name); 
         }
         return _cache[name];
    }
   
    Person._internal(this.name);
}

通常，Dart会将任何 _construction 视为班级或班级的私有对象包含它的库。例如，您可以定义为这样的全局函数：

In general Dart treats any _construction as private to either the class or the library that contains it. For example you can define as a global function like this:

_globalToThisLibaryOnly() {
    print("can only be called globally within this #library");
}

可以从定义它的库中获取的任何文件中调用。

which can be called from any file that is sourced within the library that defines it.

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