PHPのエラー『Warning: Cannot Assign by Reference』の解決方法

<?php
$var = &42; // Warning: Cannot assign by reference to a non-variable
?>

<?php
$var = &(1 + 1); // Warning: Cannot assign by reference to a non-variable
?>

<?php
function getValue() {
    return 42;
}

$var = &getValue(); // Warning: Cannot assign by reference to a non-variable
?>

<?php
$array = [1, 2, 3];
$var = &$array[0]; // これはエラーにならないが、リテラル値を参照代入するとエラーになる
?>

<?php
class MyClass {
    public $property = 42;
}

$obj = new MyClass();
$var = &$obj->property; // これはエラーにならないが、リテラル値を参照代入するとエラーになる
?>

<?php
$string = 'Hello, World!';
$var = &$string[0]; // これはエラーにならないが、リテラル値を参照代入するとエラーになる
?>

<?php
$array = [1, 2, 3, 4, 5];
$var = &array_slice($array, 0, 3); // Warning: Cannot assign by reference to a non-variable
?>

<?php
$array = [1, 2, 3, 4, 5];
$var = &array_filter($array, function($value) {
    return $value > 2;
}); // Warning: Cannot assign by reference to a non-variable
?>

<?php
$array = [1, 2, 3, 4, 5];
$var = &array_map(function($value) {
    return $value * 2;
}, $array); // Warning: Cannot assign by reference to a non-variable
?>

<?php
$array = [1, 2, 3, 4, 5];
$var = &array_reduce($array, function($carry, $item) {
    return $carry + $item;
}, 0); // Warning: Cannot assign by reference to a non-variable
?>

<?php
$array = [3, 1, 4, 1, 5, 9];
$var = &sort($array); // Warning: Cannot assign by reference to a non-variable
?>

<?php
$array = [1, 2, 3, 4, 5];
$var = &array_reverse($array); // Warning: Cannot assign by reference to a non-variable
?>