In PHP, if you want the function to modify the original array itself, you need to implement it through reference passing. The specific method is to add an & symbol before the parameter name when defining function parameters, so that the internal operations of the function directly affect external variables. For example: function modifyArray(&$arr) { $arr[] = 'new element'; }, after calling modifyArray($myArray), $myArray will be modified. Notes include: 1. There is no need to add &;2. The temporary value cannot be used as a reference parameter; 3. The reference parameters may affect the readability of the code, and it is recommended to add comments. Reference delivery is suitable for scenarios such as modifying large arrays, sharing data structures, or implementing specific design patterns. Although similar effects can also be achieved by returning new arrays, using reference passes is simpler and more efficient.

In PHP, if you want to pass an array to a function and let this function modify the original array itself (not its copy), you need to pass by reference. PHP defaults to passing parameters by value, but you can implement reference passing in some ways.

Basic practice: Use & symbols

The most direct way is to prepend the & name when defining function parameters. This way the parameter will be passed in reference form, and any operation on the variable inside the function will affect the original variable outside.

For example:

 function modifyArray(&$arr) {
    $arr[] = 'new element';
}

$myArray = [1, 2, 3];
modifyArray($myArray);
print_r($myArray); // The output contains new elements

In this example, $myArray is successfully passed into the function as a reference and modified inside the function.

Notes and common misunderstandings

• There is no need to add & when calling : Starting from PHP 5, reference passing has been specified in the function definition. Do not write & when calling, otherwise it may cause errors or warnings.
• Temporary values ??cannot be used as reference parameters : for example, modifyArray([1,2,3]) will report an error because the passed is a temporary array and there are no variables to reference.
• Reference parameters will affect readability : if others look at your code, it may not be easy to find that a function will modify the variables passed in. It is recommended to state it in the documentation or comments.

Examples of usage scenarios

Reference passes are commonly used in the following situations:

• Modify the contents of large arrays without copying the entire array
• Share and modify the same data structure between multiple functions
• Implement certain design patterns (such as observer mode)

To give an example of a practical point: you have a function that processes user lists, which will filter, sort or add additional information to the original array. This is appropriate to pass it with references.

Other alternatives (not recommended)

Although similar effects can also be achieved by returning a new array, for example:

 function addElement($arr) {
    $arr[] = 'new';
    return $arr;
}

$myArray = addElement($myArray);

However, this method needs to be assigned back every time, especially when frequently modifying the array, it will appear verbose and slightly inefficient (especially when there are large data volumes).

In general, adding & before function parameters is the most concise and effective way. As long as you pay attention to not abuse it, it will basically meet most of the needs.

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