substr with null length

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

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

The reason for this behavioral inconsistency is that when mb_substr()'s
behavior has been changed[1], substr()'s has not. Due to the subtle BC
break, in my opinion, this shouldn't have been changed in a revision
(happened for 5.4.8); a major version is more suitable for such changes.

I'd be happy to write the RFC […]

It seems to me that an RFC would be overkill for this change, but it has
to be discussed.

Tentatively, I'm +0.5 on this change.

[1]
https://github.com/php/php-src/commit/352a1956b60059f9792cac840d57b184c7305667

--
Christoph M. Becker