Uniform variable syntax in PHP 7

In older versions of PHP, variable syntax was inconsistent and could be confusing. For example, expressions like ${$first['name']} created ambiguity in parsing order. PHP 7 introduced Uniform Variable Syntax to resolve these inconsistencies by enforcing left-to-right evaluation.

The uniform variable syntax evaluates variables from left to right and requires proper use of curly brackets for clarity −

echo ${$first['name']};

This syntax allows new combinations of operators but may break backward compatibility in expressions that relied on older evaluation patterns.

Function Expression Example

With uniform variable syntax, you can immediately invoke function expressions −

<?php
$x = (function() {
    return 20 - 10;
})();
echo "$x<br>";
?>

10

New Syntax Combinations

The uniform variable syntax enables several new combinations that weren't possible before −

// Function call on array result
$foo(['bar'])();

// Property access on array element
[$obj, $obj1][0]->property;

// Static property access with dynamic class
$foo['bar']::$baz;

Nested Method and Function Calls

You can chain multiple function calls by doubling up parentheses −

foo()();           // Function returning callable
$foo->bar()();     // Instance method returning callable  
Foo::bar()();      // Static method returning callable
$foo()();          // Variable function returning callable

Arbitrary Expression Dereferencing

Any valid expression can now be dereferenced using parentheses −

(expression)['foo'];    // Access array key
(expression)->foo;      // Access property
(expression)->foo();    // Call method

Chained Function Example

Here's a practical example demonstrating nested function calls −

<?php
function emp() {
    echo "This is emp() <br>";
}

function dept() {
    echo "This is dept() <br>";
    return 'emp';
}

function sub() {
    echo "This is sub()<br>";
    return 'dept';
}

sub();
echo "----------------<br>";
sub()();
echo "----------------<br>";
sub()()();
?>

This is sub()
----------------
This is sub()
This is dept()
----------------
This is sub()
This is dept()
This is emp()

Conclusion

Uniform Variable Syntax in PHP 7 provides consistent left-to-right evaluation, enabling powerful new syntax combinations like chained function calls and expression dereferencing, though it may break some legacy code patterns.