dart - 为什么 Dart 有编译时常量？

Question

Dart 有编译时常量的概念。编译时常量在编译时被解析和创建，并被规范化。

例如，这里是 const Point 的构造函数:

class Point {
  final num x, y;
  const Point(this.x, this.y);
}

以下是您如何使用它:

main() {
  var p1 = const Point(0, 0);
  var p2 = const Point(0, 0);
  print(p1 == p2); // true
  print(p1 === p2); // true
}

这是一个不明显的特性，与其他动态语言中的特性似乎没有相似之处。 const有限制对象，就像所有字段都必须是 final 并且它必须有一个 const 构造函数。

为什么 Dart 有编译时常量？

Answer 1

来自 mailing list , 弗洛里安·洛伊奇 (Florian Loitsch) 写道:

The canonicalization property of compile-time constants is nice, but not the main-reason to have them. The real benefit of compile-time constants is, that they don't allow arbitrary execution at construction and can therefore be used at places where we don't want code to executed. Static variables initializers, for example, were initially restricted to compile-time constants to avoid execution at the top-level. In short, they make sure that a program starts with 'main' and not somewhere else.