Generator::rewind
(PHP 5 >= 5.5.0, PHP 7, PHP 8)
Generator::rewind — 重置迭代器
说明
public Generator::rewind(): void
如果迭代已经开始了，这里会抛出一个异常。
参数
此函数没有参数。
返回值
没有返回值。
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User Contributed Notes 2 notes
i'm pati on stackoverflow ¶
6 years ago
Actually, this method can be useful to test a generator before iterating, as it executes your function up to the first yield statement. I.e. if you try to read a non-existent file in a generator, an error will normally occur only in client code foreach()'s first iteration. Sometimes this can be critical to check beforehand.
Take a look at a modified example from here:
http://php.net/manual/ru/language.generators.overview.php#112985
<?php
function getLines($file) {
$f = fopen($file, 'r');
try {
while ($line = fgets($f)) {
yield $line;
}
} finally {
fclose($f);
}
}
$getLines = getLines('no_such_file.txt');
$getLines->rewind(); // with ->rewind(), a file read error will be thrown here and a log file will not be cleared
openAndClearLogFile();
foreach ($getLines as $n => $line) { // without ->rewind(), the script will die here and your log file will be cleared
writeToLogFile('reading: ' . $line . "\n");
}
closeLogFile();
?>
P.S.: When you iterate over a generator after ->rewind(), you'll get the first yielded value immediately, as the preceding code was already executed.
uther at somewherebetweennowhere dot net ¶
6 years ago
I'm guessing the *only* purpose for this even existing is so that it is compatible with the Iterator interface o_O