如何在没有foreach的情况下使用PHP生成器？

这是一个简单的 JavaScript生成器(来自： http://blog.carbonfive.com/2013/12/01/hanging-up-on-callbacks-generators-in-ecmascript-6/)

function* powGenerator() {
  var result = Math.pow(yield "a",yield "b");
  return result;
}

var g = powGenerator();
console.log(g.next().value);   // "a",from the first yield
console.log(g.next(10).value); // "b",from the second
console.log(g.next(2).value);  // 100,the result

我正在尝试使用类似于PHP的模型,但这有点令人头疼.

<?PHP
function powGenerator() {
  return pow((yield 'a'),(yield 'b'));
}

在我走得更远之前,我在PHP中遇到了这个错误

Fatal error: Generators cannot return values using “return”

好吧,也许我会用另一个产量来获得最终价值？ …

<?PHP
function powGenerator() {
  yield pow((yield 'a'),(yield 'b'));
}

$g = powGenerator(); //=> Generator {#180}
echo $g->send(10);   //=> "b"
echo $g->send(2);    //=> 100

好的,所以我恢复了价值,但这里有两个主要问题

>我的“a”去了哪里？ – 注意在JS示例中,我能够访问“a”和“b”产生的值以及100个最终结果.
>发电机还没有完成！ – 我必须拨打额外的时间来完成发电机

$g->valid();   //=> true
$g->send('?'); //=> null
$g->valid();   //=> false

来自PHP Generator::send

public mixed Generator::send ( mixed $value )

Sends the given value to the generator as the result of the current yield expression and resumes execution of the generator.

If the generator is not at a yield expression when this method is called,it will first be let to advance to the first yield expression before sending the value. As such it is not necessary to “prime” PHP generators with a 07002 call (like it is done in Python).

强调“因此没有必要使用Generator :: next()来”启动“PHP生成器”.好的,但这究竟意味着什么？我没有像JavaScript示例那样“填充”它,但是第一个产生的值也被吞噬了.

任何人都可以解释你是如何在不使用foreach的情况下逐步完成生成器的吗？

$g = powGenerator();
echo $g->current(); //a

function powGenerator() {
    yield pow((yield 'a'),(yield 'b'));
    echo "Okay,finishing here Now!\n";
}

$g = powGenerator();
echo $g->current(),"\n"; //a
echo $g->send(10),"\n";  //b
echo $g->send(2),"\n";   //100
$g->next();               // Resumes execution of the generator,// which prints its own message and completes.
var_dump($g->valid());    //false

a
b
100
Okay,finishing here Now!
bool(false)

function powGenerator() {
    return pow((yield 'a'),(yield 'b'));
    echo "This will never print.";
}

$g = powGenerator();
echo $g->current(),"\n";   // Prints just the newline,you're moving on
                          // to a return which you must get explicitly.
var_dump($g->valid());    // Generator complete,you're free to get the return.
echo $g->getReturn(),"\n";

a
b

bool(false)
100

function letterGenerator() {
    yield from range('a','z');
}

$g = letterGenerator();

while ($g->valid()) {
    echo $g->current();
    $g->next();
}

abcdefghijklmnopqrstuvwxyz