Why Can't I Access Array Values Using Expressions in PHP?

Dynamic Array Access in PHP [Original: Access Array Value on the Fly]

PHP provides the ability to access array values using bracket notation ([]). However, a common pain point is the inability to achieve this directly when working with expressions.

Problem:

In the following example, attempting to access an array value using an expression within bracket notation results in an error:

echo array('a', 'b', 'c')[$key];

Solution:

The reason for this error is a limitation in PHP's grammar. Subscript notation is only valid for variable expressions, not general expressions. To overcome this, you can use an intermediary variable:

$variable = array('a', 'b', 'c');
echo $variable[$key];

Technical Explanation:

PHP's grammar does not allow subscript notation on expressions. This means that you cannot apply it to the result of a function call, parentheses, or other expressions. This behavior differs from other languages where it is possible to resolve subscripts against expressions.

Additional Examples of Invalid Subscripts:

$x = array(1, 2, 3);
print ($x)[1]; // Invalid: Subscripted expression is a parenthetical expression.

function ret($foo) { return $foo; }
echo ret($x)[1]; // Invalid: Subscripted expression is a call expression.

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