为什么在注释中声明PHP变量类型？

Question

I'm fairly new to PHP, and I just started using NetBeans to develop my PHP code.

Out of the blue, as I entered a variable in a query, a dialog popped up and asked me to complete a comment to hold the variable type. I did some investigation and found that this seems to be a popular feature of NetBeans, but I couldn't find any information to explain to me why this was the case.

Why would someone want to place a PHP variable's type in a comment? Is it for development use, or does it actually benefit the code itself? Is it integral, or optional?

Answer 1

Adding the type in a @var tag inside your method's comment will allow NetBeans to show you code completion. This of course is optional but it is always a good idea to fully document your code.

Edit: A tip for NetBeans to auto-generate the comments for you is to use the /** expansion. To do this, simply place the cursor above the property or method you want to document and type /** and then press the ENTER key. This will expand a phpDoc style comment and add the appropriate tags.

Edit 2: You can use the @var tag on a property and you can use the @param tag on a method to achieve the same effect with parameters passed into a method.

Use of the @var tag on a property will give you code hints while using the property any where it is visible:

/**
 *
 * @var My_Type
 */
private $_myProperty;

Use of the @param tag on a method will give you code hints while using the parameter inside the method:

/**
 *
 * @param My_Type $obj 
 */
public function myMethod($obj) {

}

Another way to achieve a similar effect while also providing a modicum of type safety is to use PHP's type hinting mechanism:

public function myMethod(My_Type $obj) {

}

Notice that this method has the type specified in the method signature. NetBeans will now provide the same code completion inside the method that is available using the @param tag and PHP will produce a E_RECOVERABLE_ERROR if the type passed into the method is not the same type that was specified. See PHP's documentation regarding errors and how to handle them if your interested in learning more about the above error.

Answer 2

I guess you're talking about something like that:

/**
 * @var SimpleXMLElement $xml
 */
private $xml;

This is so called phpDoc comment . It allows you to generate API documentation ( like this one for instance ). Furthermore, most IDEs including Eclipse and NetBeans also support that syntax, and provide dynamic code completion etc.

Answer 3

If you want to declare the type of a variable in the case where the variable is not a class property but just a variable that holds some returned value, use single star comments followed by @var followed by your variable name and finally followed by the type of that variable . For example:

/* @var $errorMessage NotificationMessage */
$errorMessage= $allMessages->rewind()->current();

will tell NetBeans or PhpStorm that $errorMessage is an instance of NotificationMessage, and you should get the code completion for that variable.

Answer 4

Despite netbeans use it for autocompletion it is often useful for documenting your code:

In this case you know what this method gets and what it returns but inside the code you have no idea what is happening

/**
 * Returns some stuff
 * @param string $someObj
 * @return array
 */
public function someMethod($someObj) {
    $factoredObj = getObject($someObj); //you are not sure what type it returns
    $resultArray = $factoredObj->toArray();
    return $resultArray;
}

You can comment it with /* @var $variable type */ inside the code

/**
 * Returns some stuff
 * @param string $someObj
 * @return array
 */
public function someMethod($someObj) {
    /* @var $factoredObj someType */
    $factoredObj = getObject($someObj);
    $resultArray = $factoredObj->toArray();
    return $resultArray;
}

or

$factoredObj = getObject($someObj); /* @var $factoredObj someType */

Answer 5

Because PHP is a loose/duck typed language, when you create a large program those type hints can help you or others understand what is going on if an issue should arise. For example, expecting a mixed type and sending an integer.