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var_dump() $return like print_r to allow using it in ob_start() callbacks without fatal #18340

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kkmuffme opened this issue Apr 16, 2025 · 6 comments
Open

var_dump() $return like print_r to allow using it in ob_start() callbacks without fatal #18340

kkmuffme opened this issue Apr 16, 2025 · 6 comments
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Feature Status: Requires RFC

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@kkmuffme
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Description

function my_cb($b) {
    ob_start();
    var_dump($b);
    $r = ob_get_clean();
    return $b . $r;
}

ob_start('my_cb');
echo "hello";

Will result in:

Fatal error: ob_start(): Cannot use output buffering in output buffering display handlers

When using:

function my_cb($b) {
    $r = print_r($b, true);
    return $b . $r;
}

it works without error (now, this wasn't the case in earlier PHP versions where it had the same issue as can be seen
in the old docs php/doc-en@e8f4c44#diff-a18323268abbc44bce515215167dfae5d0fb378c63ea36bea0f6e537a6a0114aL115)

What's the reason why print_r with return (which uses buffering internally) can be called in an ob callback now, but ob_start still can't?
Anyway though - given this, var_dump should have a 2nd argument $return to allow returning, so it can be used in ob_start callbacks, where ob_start cannot be used to get it's value
@MorganLOCode
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One of the problems with giving var_dump a second argument is that it already takes an arbitrary number of arguments.

@kkmuffme
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Oh right, how about a new var_return or var_dump_return then?

@Piskvor
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Piskvor commented Apr 25, 2025

@kkmuffme : That's literally var_export($whatever, true);.

https://www.php.net/manual/en/function.var-export.php

@kkmuffme
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It's not, the output of var_export and var_dump are completely different.

@nielsdos
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Oh right, how about a new var_return or var_dump_return then?

That would require an RFC.

@staabm
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staabm commented Apr 30, 2025 •
edited
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Fatal error: ob_start(): Cannot use output buffering in output buffering display handlers

interessting.. never seen this error.. are more functions then var_dump affected by this ?

edit: ohh I see.. the problem is not var_dump, but the ob_start() usage from within the callback passed to ob_start() at a different call-site

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@staabm @Piskvor @nielsdos @kkmuffme @MorganLOCode