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Generator::rewind

(PHP 5 >= 5.5.0, PHP 7, PHP 8)

Generator::rewindイテレータを巻き戻す

説明

public Generator::rewind(): void

既に処理が始まっている場合は、例外をスローします。

パラメータ

この関数にはパラメータはありません。

戻り値

値を返しません。

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User Contributed Notes 2 notes

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20
i'm pati on stackoverflow
7 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.
up
-18
uther at somewherebetweennowhere dot net
8 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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