方法级联如何在 dart 中准确工作? [英] How do method cascades work exactly in dart?

问题描述

如飞镖文章所述:

.."语法调用方法(或 setter 或 getter)但丢弃结果，并返回原始接收器.

The ".." syntax invokes a method (or setter or getter) but discards the result, and returns the original receiver instead.

所以我认为这会起作用:

So I assumed that this would work:

myList..clear().addAll(otherList);

这给了我一个错误，我不能在 null 上调用 .addAll.

which gave me the error that I can't call .addAll on null.

很明显 . 在 .. 之前，所以 .addAll 已经在 的 result 上被调用>.clear().

So apparently . precedes .. so that .addAll has been invoked on the result of .clear().

我现在想我有两种可能来写这个:

I figure now that I have two possibilities to write this:

1. myList..clear()..addAll(otherList);
2. (myList..clear()).addAll(otherList);(如果我想得到.addAll()的结果.

1. myList..clear()..addAll(otherList);
2. (myList..clear()).addAll(otherList); (If I wanted to get the result of .addAll().

这是正确的吗?如果是，为什么决定给 . 优先?这似乎非常违反直觉.是否要避免这样的语法:myList(..clear().useResultOfClear()).addAll(otherList);?

Is this correct? If yes, why the decision to give . precedence? It seems very counterintuitive. Is it to avoid syntax like this: myList(..clear().useResultOfClear()).addAll(otherList);?

推荐答案

您可以阅读 Gilad Bracha 的文章:Dart 中的方法级联.在它的结尾，您会看到许多示例.

You can read the article from Gilad Bracha : Method Cascades in Dart. At its ends, you will see many examples.

另见 Lasse Nielsen 的这个回答运算符优先级 :

将.."视为不是真正的运算符，而更像是范围结构(如括号)会有所帮助.它创建一个从.."到下一个.."或第一个其他范围分隔符(;"、)"、}"或类似的范围)的新范围.

It helps to think of ".." as not really an operator, but more like a scoping construct (like parentheses). It creates a new scope from the ".." to either the next "..", or the first other scope delimiter (";", ")", "}" or similar).

基本上，a..b().c() 和 (t){t.b().c();return t;}(a)

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