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

down

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.

down

-16

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

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官方地址：https://www.php.net/manual/en/generator.rewind.php

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Generator::rewind

说明

参数

返回值

User Contributed Notes 2 notes