为什么Dart不继承构造函数？ [英] Why Dart does not inherit constructor?

问题描述

我来自PHP世界，好奇为什么开发人员选择不添加构造函数（使用arg）继承。从我的观点，它违反了DRY原则通过重复大量的代码，取决于结构。我做了很少的研究 - PHP，Ruby，Python继承了构造函数。 Java，C＃，C ++不。 C ++ 0x具有显式定义继承的新功能。

I am coming from PHP world and am curious why developers choose the way not adding constructor (with arg) to inheritance. From my view it violates DRY principle by repeating a lot of code, depending on structure. I did little research - PHP, Ruby, Python inherits constructor. Java, C#, C++ not. C++0x have new feature explicitly defining inheritances.

那么，对于没有构造函数继承和明确写入构造函数的程序员来说，有什么优势吗？

So is there any advantage for programmer not having constructor inherited and explicitly write constructor again and again?

推荐答案

我想你可能需要问Dart的设计师提出问题，但是从继承树中省略构造函数的典型原因是，具有需要发生的特定构造时操作。在java中（例如），所有对象都继承自Object，它有一个零值构造函数。

I think you'd probably have to ask Dart's designers that question, but the typical reason for omitting constructors from the inheritance tree is that a class may have specific construct-time operations that need to happen. In java (for example), all objects inherit from Object, which has a zero value constructor.

所以如果你想创建一个这样的对象：

So if you wanted to create some object like this:

public class Foo {
   private final String bar;

   public Foo(String barValue) {
       this.bar = barValue;
   }
}

当有人调用父的零参数构造函数时发生：

You'd be left with some uncertainty as to what happens when someone called the parent's zero parameter constructor:

Foo bla = new Foo(); // runtime error or is bar null?

当然，与所有语言功能一样，您可以想出这种行为可以被指定的方式，但显然java和dart的设计师不喜欢任何他们。

Of course, as with all language features, you can think of ways that this behavior could be specified, but clearly java and dart's designers didn't like any of them.

最后，我认为这一切归结为哲学：php，ruby等，去在减少打字的方向，因为java，C＃，dart等，倾向于在更多的打字方向，更少的混乱的空间。

In the end, I think it all comes down to philosophy: php, ruby, etc., goes in the direction of less typing where as java, C#, dart, etc., tend to go in the direction of more typing and less room for confusion.

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