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In-Reply-To: <CAJaRsPvTvZVWtszNH-uqaOc8487ncGjKdgFikzq60gUhvTNMtQ@mail.gmail.com>
Date: Mon, 21 Oct 2019 17:28:56 +0200
Message-ID: <CAF+90c8=Fd2eaEB=fRGe=GtD7S89__VT5v7LnCR92-CM8vZbGQ@mail.gmail.com>
To: "Colin O'Dell" <colinodell@gmail.com>
Cc: PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="00000000000092167f05956d5803"
Subject: Re: [PHP-DEV] substr with null length
From: nikita.ppv@gmail.com (Nikita Popov)

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On Mon, Oct 21, 2019 at 5:03 PM Colin O'Dell <colinodell@gmail.com> wrote:

> Hello Internals,
>
> Is there any particular reason why the substr() function doesn't accept a
> null $length like mb_substr() does?  It seems the behavior to read through
> the end of the string can only be controlled by the presence or absence of
> the $length parameter:  https://3v4l.org/YpuO1
>
> I discovered this discrepancy between the two methods while attempting to
> create a specialized string wrapper class with a method like this:
>
>     public function getSubstring(int $start, ?int $length = null): string
>     {
>         if ($this->isMultibyte) {
>             return mb_substr($this->line, $start, $length,
> $this->encoding);
>         } else {
>             return substr($this->line, $start, $length);
>         }
>     }
>
> This method would not work as expected without additional boilerplate like:
>
>     public function getSubstring (int $start, ?int $length = null): string
>     {
>         if ($this->isMultibyte) {
>             return mb_substr($this->line, $start, $length,
> $this->encoding);
>         } elseif ($length === null) {
>             return substr($this->line, $start);
>         } else {
>             return substr($this->line, $start, $length);
>         }
>     }
>
> Or:
>
>     public function getSubstring (int $start, ?int $length = null): string
>     {
>         if ($this->isMultibyte) {
>             return mb_substr($this->line, $start, $length,
> $this->encoding);
>         } else {
>             return substr($this->line, $start, $length ??
> (strlen($this->line) - $start));
>         }
>     }
>
> Are there any historical reasons preventing substr() from accepting a null
> $length like mb_substr() does?  I'd be happy to write the RFC and take a
> stab at the implementation if there's interest in such a change.
>

This is a fairly common deficiency in the implementation of internal
functions. Part of the reason is that historically zend_parse_parameters
did not support the ! modifier for integers, and partly these are just
implementation oversights.

Feel free to send a PR to fix this for PHP 8, no RFC needed. If you're
interested in addressing this for more functions, do a grep for "= UNKNOWN"
on the codebase, which gives you (with a few exceptions) a list of
functions that currently handle null parameters incorrectly and should
ideally be fixed for PHP 8.

Nikita

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