具有专用标识符参数的符号 [英] Symbol with private identifier argument

问题描述

我想创建一个与私有MethodMirror的简单名称相同的符号。但是，Symbol的文档指出，新Symbol的参数必须是有效的公共标识符。如果我尝试创建一个 const Symbol（'_ privateIdentifier'） dart编辑器，则通知我该常量表达式的求值将引发异常-尽管程序运行正常，我

I want to create a symbol equal to that of a private MethodMirror's simplename. However, Symbol's documentation states the argument of new Symbol must be a valid public identifier. If I try and create a const Symbol('_privateIdentifier') dart editor informs me that evaluation of this constant expression will throw an exception - though the program runs fine, and I am able to use it without any issues.

void main(){
  //error flagged in dart editor, though runs fine.
  const s = const Symbol('_s');
  print(s); //Symbol("_s");
}

似乎镜像系统使用符号。

It seems the mirror system uses symbols.

import 'dart:mirrors';
class ClassA{
  _privateMethod(){}
}

void main(){
  var classMirror = reflect(new ClassA()).type;
  classMirror.declarations.keys.forEach(print);
  //Symbol("_privateMethod"), Symbol("ClassA")
}

由于过时的飞镖分析器，飞镖编辑器中的文档/错误标记是否是遗留错误？还是将来有计划执行此公共要求？还有另一种方法来创建唯一的标识符号，该标识符号将被最小化为与声明的简单名称相同的符号

Is the documentation/error flagging in dart editor a legacy bug due to an outdated dart analyzer? Or are there plans to enforce this public requirement in future? Is there another way to create a unique identifying symbol that will be minified to the same symbol as the declaration's simple name

推荐答案

不会抛出异常，则VM会在const Symbol构造函数中出现错误。

If it doesn't throw then the VM has a bug in the const Symbol constructor.

问题在于， _ s无法标识私有变量，而又不说出它是哪个库属于。由于这个原因，符号构造函数有第二个参数采用 LibraryMirror ，并且传递私有名称而不传递镜像也应该抛出异常。
如果不回避const构造函数的要求（不执行代码！），这在const构造函数中很难做到，这很可能是VM无法处理的原因。

The problem is that "_s" does not identify a private variable without also saying which library it belongs to. The symbol constructor has a second argument taking a LibraryMirror for that reason, and passing in a private name without also passing in a mirror should throw. That's hard to do in a const constructor without side-stepping the requirements of a const constructor (no executing code!), which is likely why the VM doesn't handle it. It needs to be special-cased at the compiler level.

您还会发现 const Symbol（'_ s'）与 #_ s 不同。后者为当前库创建一个私有符号，前者（如果运行）创建一个名为 _s的非私有符号，这实际上没有用。例如 print（identical（#_ s，const Symbol（'_ s'）））; 打印false。

You will also find that const Symbol('_s') is not the same as #_s. The latter creates a private symbol for the current library, the former (if it runs) creates a non-private symbol with the name '_s', which is not really useful. For example print(identical(#_s, const Symbol('_s'))); prints false.

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