在Dart中切换失败 [英] Switch fallthrough in Dart

问题描述

我从今天开始学习Dart，遇到了一些我的Google技能很难找到的东西。

I started learning Dart today, and I've come across something that my google skills are having trouble finding.

我怎么会陷入困境非空的情况？

How do I have a fall-through in a non-empty case?

我的用例是这样的：我正在编写sprintf实现（因为dart也没有此实现），除此以外它都可以工作跌倒的东西。解析变量类型时，例如，可以使用％x和％X，其中大写类型告诉格式化程序输出应该是大写的。

My use case is this: I'm writing a sprintf implementation (since dart doesn't have this too), which would work except for this fall-through thing. When parsing the variable type you can, for example, have "%x" versus "%X" where the upper case type tells the formatter that the output is supposed to be uppercase.

半伪代码如下：

bool is_upper = false;
switch (getType()) {
    case 'X':
      is_upper = true;
    case 'x':
      return formatHex(is_upper);
}

我可以想到的另一种方法是，以下一种方法

The other ways I can think of doing this, would one of the following

1：

switch (getType()) {
  case 'X': case 'x':
    return formatHex('X' == getType());
}

2：

var type = getType();
if (type in ['x', 'X']) {
   return formatHex('X' == getType());
}

现在，第二种选择看起来不错，但是您必须记住有11种情况，这意味着要有11个 if（在[]中键入），这是我想要的更多类型。

Now, the second choice almost looks good, but then you have to remember that there are eleven cases, which would mean having eleven if (type in []), which is more typing that I'd like.

所以，飞镖有一些我不知道的 /// $ FALL-THROUGH $ 吗？

So, does dart have some // //$FALL-THROUGH$ that I don't know about?

谢谢。

推荐答案

Dart规范为开关盒提供了一种继续使用另一个开关盒的方式使用继续：

The Dart specification gives a way for a switch case to continue to another switch case using "continue":

switch (x) {
  case 42: print("hello");
           continue world;
  case 37: print("goodbye");
           break;
  world:  // This is a label on the switch case.
  case 87: print("world");
}

它可在VM中使用，但可惜的是dart2js开关的实现尚未实现支持该功能。

It works in the VM, but sadly the dart2js switch implementation doesn't yet support that feature.

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