Why Can't I Access Array Values Dynamically in PHP with a Single Line?

Understanding Array Value Access on the Fly in PHP

In PHP, accessing array values dynamically has presented a challenge for developers seeking efficient one-liners. This issue arises when attempting to map a variable using an array within a single line of code. While the desired syntax, like echo array('a','b','c')[$key];, results in an error, a workaround using an intermediary variable like $variable = array('a','b','c'); echo $variable[$key]; becomes necessary.

While this method resolves the immediate problem, it introduces an unnecessary variable. To delve into the technical reason behind this limitation, PHP's grammar restricts subscript notation to variable expressions, not general expressions. This grammar differs from many other programming languages that allow subscripting on any expression.

Interestingly, PHP's grammar encompasses additional cases where subscripting on non-variable expressions results in invalid syntax, such as:

$x = array(1,2,3);
print ($x)[1]; //illegal, on a parenthetical expression, not a variable exp.

function ret($foo) { return $foo; }
echo ret($x)[1]; // illegal, on a call expression, not a variable exp.

While the inability to subscript arbitrary expressions in PHP may be viewed as a deficiency, it could stem from limitations of the parser generator employed or a desire to maintain backward compatibility.

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