Upgrading to PHP 7

Chapter 4. Basic Language Changes

PHP 7.0 introduces numerous small changes to the language, new operators, functions, and changes to existing functions and constructs.

Operators

PHP 7.0 adds two new operators, the null coalesce operator and the combined comparison operator.

Null Coalesce Operator

The new null coalesce operator ?? will return the left operand if it is not null; otherwise, it returns the right operand. The most interesting part of this operator is that it will not emit a notice if the operand is a nonexistent variable—similar to isset().

Effectively, this is a shortcut for isset() combined with a ternary for assignment. Example 4-1 shows this new, more compact syntax compared to the older syntax.

Example 4-1. Null coalesce operator

$foo = isset($bar) ? $bar : $baz;

$foo = $bar ?? $baz;

The two lines in the preceding example are functionally identical.

You can also nest the operator, and it will return the first non-null (or the last argument), as shown in Example 4-2.

Example 4-2. Nested null coalesce operators

$config =   $config ??
            $this->config ??
            static::$defaultConfig; 

This shows a common fall-through scenario, whereby a local configuration may be set in $config, otherwise fallback to the instance level $this->config, or finally, fall back to the static defaults ...