Is it necessary to declare types in PHP when passing variables by reference?

In PHP, it is not necessary to declare types when passing variables by reference. PHP is a dynamically typed language, so the type of a variable is determined at runtime. When passing variables by reference, you simply use the `&` symbol before the variable name to indicate that it is being passed by reference. 

function modifyValue(&$value) {
    $value = $value * 2;
}

$num = 5;
modifyValue($num);
echo $num; // Output will be 10

Keywords

PHP type declaration pass by reference variables function parameters

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