生成器委托

PHP7中支持delegating generator，可以自动展开subgenerator;

A “subgenerator” is a Generator used in the portion of the yield from syntax.

我们需要在PHP5支持子生成器，将子生成器最后yield值作为父生成器yield表达式结果，仅只需要加两行代码，递归的产生一个AsyncTask对象来执行子生成器即可。

  1. <?php
  3. final class AsyncTask
  4. {
  5.     public function next($result = null)
  6.     {
  7.         $value = $this->gen->send($result);
  9.         if ($this->gen->valid()) {
  10.             if ($value instanceof \Generator) {
  11.                 $value = (new self($value))->begin();
  12.             }
  13.             return $this->next($value);
  15.         } else {
  16.             return $result;
  17.         }
  18.     }
  19. }
  1. <?php
  2. function newSubGen()
  3. {
  4.     yield 0;
  5.     yield 1;
  6. }
  8. function newGen()
  9. {
  10.     $r1 = (yield newSubGen());
  11.     $r2 = (yield 2);
  12.     echo $r1, $r2;
  13.     yield 3;
  14. }
  15. $task = new AsyncTask(newGen());
  16. $r = $task->begin(); // output: 12
  17. echo $r; // output: 3