## Other changes

### Notices and warnings on arithmetic with invalid strings

New `E_WARNING` and `E_NOTICE` errors have been introduced when invalid strings are coerced using operators expecting numbers (`+` `-` `*` `/` `**` `%` `<<` `>>` `|` `&` `^`) or their assignment equivalents. An `E_NOTICE` is emitted when the string begins with a numeric value but contains trailing non-numeric characters, and an `E_WARNING` is emitted when the string does not contain a numeric value.

`<?php
'1b' + 'something';`

The above example will output:

    Notice: A non well formed numeric value encountered in %s on line %d
    Warning: A non-numeric value encountered in %s on line %d

### Warn on octal escape sequence overflow

Previously, 3-octet octal string escape sequences would overflow silently. Now, they will still overflow, but `E_WARNING` will be emitted.

`<?php
var_dump("\500");`

The above example will output:

    Warning: Octal escape sequence overflow \500 is greater than \377 in %s on line %d
    string(1) "@"

### Inconsistency fixes to `$this`

Whilst `$this` is considered a special variable in PHP, it lacked proper checks to ensure it wasn't used as a variable name or reassigned. This has now been rectified to ensure that `$this` cannot be a user-defined variable, reassigned to a different value, or be globalised.

### Session ID generation without hashing

Session IDs will no longer be hashed upon generation. With this change brings about the removal of the following four ini settings:

- `session.entropy_file`
- `session.entropy_length`
- `session.hash_function`
- `session.hash_bits_per_character`

And the addition of the following two ini settings:

- `session.sid_length` - defines the length of the session ID, defaulting to 32 characters for backwards compatibility)
- `session.sid_bits_per_character` - defines the number of bits to be stored per character (i.e. increases the range of characters that can be used in the session ID), defaulting to 4 for backwards compatibility

### Changes to INI file handling

`precision`

  If the value is set to -1, then the dtoa mode 0 is used. The default value is still 14.

`serialize_precision`

  If the value is set to -1, then the dtoa mode 0 is used. The value -1 is now used by default.

`gd.jpeg_ignore_warning`

  The default of this php.ini setting has been changed to 1, so by default libjpeg warnings are ignored.

`opcache.enable_cli`

  The default of this php.ini setting has been changed to 1 (enabled) in PHP 7.1.2, and back to 0 (disabled) in PHP 7.1.7.

### Session ID generation with a CSPRNG only

Session IDs will now only be generated with a CSPRNG.

### More informative TypeError messages when `NULL` is allowed

TypeError exceptions for arg_info type checks will now provide more informative error messages. If the parameter type or return type accepts `NULL` (by either having a default value of `NULL` or being a nullable type), then the error message will now mention this with a message of "must be ... or null" or "must ... or be null."