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Date: Tue, 18 Feb 2020 12:20:18 +0100
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To: PHP internals <internals@lists.php.net>
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Subject: Make var_dump() use serialize_precision
From: nikita.ppv@gmail.com (Nikita Popov)

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Hi internals,

https://github.com/php/php-src/pull/5172 changes var_dump() to use
serialize_precision instead of precision to dump floating-point numbers.

To recap: serialize_precision defaults to -1, which will print exactly as
many floating-point digits as are needed to represent the number
accurately. precision defaults to 14, which will print a shorter but
potentially inaccurate float representation.

The motivation here is that var_dump() is debugging functionality and
should print values as accurately as possible. The single most common bug
report we receive is some kind of variation on:

    $sum = 0.1 + 0.2;
    var_dump($sum); // float(0.3)
    var_dump($sum == 0.3); // bool(false) WTF???

After this change, this would instead be:

    $sum = 0.1 + 0.2;
    var_dump($sum); // float(0.30000000000000004)
    var_dump($sum == 0.3); // bool(false) Makes sense...

I have little hope that developers will suddenly start understanding
floating-point numbers, but at least this should reduce the amount of
confusion.

Does anyone see an issue with doing this change?

Regards,
Nikita

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