I have the class name Car stored as a static variable in constants. I would like to use this constant to call the function a. One options is to use an intermediate variable $tmp. I could then call $tmp::a(). Is there a way to do this in one statement? My attempt is below.
class Car{
public static function a(){
return 'hi';
}
}
class Constants{
public static $use='Car';
}
$tmp=Constants::$use;
echo(${Constants::$use}::a());
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Output is as follows
PHP Notice: Undefined variable: Car in /home/mU9w5e/prog.php on line 15
PHP Fatal error: Class name must be a valid object or a string in /home/mU9w5e/prog.php on line 15
There is always call_user_func():
echo call_user_func( array( Constants::$use, 'a'));
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The only alternative that I could find to #nickb's way was using something I've never heard of, but hey that's what SO is for!
I found the ReflectionMethod, which seems to be more bloated than the call_user_func, but was the only alternative way that I could find:
<?php
class Car{
public static function a(){
return 'hi';
}
}
class Constants{
public static $use='Car';
}
$reflectionMethod = new ReflectionMethod(Constants::$use, 'a');
echo $reflectionMethod->invoke(new Car());
The above is a bit of a failed experiment as Casebash doesn't want to create temp variables.
As CORRUPT mentioned in the comments, it is possible to use the following although was tested on PHP version 5.4.14 (which I am unable to do):
echo (new ReflectionMethod(Constants::$use, 'a'))->invoke(new Car());
I have crazy solution, but you should never use it :^ )
echo ${${Constants::$use} = Constants::$use}::a();
Related
This question already has answers here:
Reference - What does this error mean in PHP?
(38 answers)
Closed 8 years ago.
So I'm refactoring my code to implement more OOP. I set up a class to hold page attributes.
class PageAtrributes
{
private $db_connection;
private $page_title;
public function __construct($db_connection)
{
$this->db_connection = $db_connection;
$this->page_title = '';
}
public function get_page_title()
{
return $this->page_title;
}
public function set_page_title($page_title)
{
$this->page_title = $page_title;
}
}
Later on I call the set_page_title() function like so
function page_properties($objPortal) {
$objPage->set_page_title($myrow['title']);
}
When I do I receive the error message:
Call to a member function set_page_title() on a non-object
So what am I missing?
It means that $objPage is not an instance of an object. Can we see the code you used to initialize the variable?
As you expect a specific object type, you can also make use of PHPs type-hinting featureDocs to get the error when your logic is violated:
function page_properties(PageAtrributes $objPortal) {
...
$objPage->set_page_title($myrow['title']);
}
This function will only accept PageAtrributes for the first parameter.
There's an easy way to produce this error:
$joe = null;
$joe->anything();
Will render the error:
Fatal error: Call to a member function anything() on a non-object in /Applications/XAMPP/xamppfiles/htdocs/casMail/dao/server.php on line 23
It would be a lot better if PHP would just say,
Fatal error: Call from Joe is not defined because (a) joe is null or (b) joe does not define anything() in on line <##>.
Usually you have build your class so that $joe is not defined in the constructor or
Either $objPage is not an instance variable OR your are overwriting $objPage with something that is not an instance of class PageAttributes.
It could also mean that when you initialized your object, you may have re-used the object name in another part of your code. Therefore changing it's aspect from an object to a standard variable.
IE
$game = new game;
$game->doGameStuff($gameReturn);
foreach($gameArray as $game)
{
$game['STUFF']; // No longer an object and is now a standard variable pointer for $game.
}
$game->doGameStuff($gameReturn); // Wont work because $game is declared as a standard variable. You need to be careful when using common variable names and were they are declared in your code.
function page_properties($objPortal) {
$objPage->set_page_title($myrow['title']);
}
looks like different names of variables $objPortal vs $objPage
I recommend the accepted answer above. If you are in a pinch, however, you could declare the object as a global within the page_properties function.
$objPage = new PageAtrributes;
function page_properties() {
global $objPage;
$objPage->set_page_title($myrow['title']);
}
I realized that I wasn't passing $objPage into page_properties(). It works fine now.
you can use 'use' in function like bellow example
function page_properties($objPortal) use($objPage){
$objPage->set_page_title($myrow['title']);
}
I am new to php so please excuse my lack of knowledge. I am using eclipse and have a project with 3 files inside the project. I am creating a find discount class which takes the class object to call a function from another class. The error:
Notice: Undefined variable: GetInfoClass line ..
Fatal error: Call to a member function getAge() on a non-object line ...
I tried to read about it but I cant seem to understand it. Please help. Thanks
formResponse:
include "GetInfo.php";
include "IfDiscount.php";
$IfDiscount= new IfDiscount();
echo $IfDiscount->findDiscount();
class IfDiscount:
class IfDiscount
{
public function findDiscount(){
$Age = $GetInfoClass->getAge();
echo $Age;}}
$GetInfoClass is not available to findDiscount() because it is out of scope. You should pass it to findDiscount() as a parameter to make it available to that method:
public function findDiscount($GetInfoClass){
$Age = $GetInfoClass->getAge();
return $Age;
}
echo $IfDiscount->findDiscount($GetInfoClass);
(You also want to return $Age, not echo it. You already explicitly echo it when you call that method.)
Is there a built-in static method or property to refer to a PHP class so that it will contextually be represented as a string? For example:
Instead of this:
$obj->tempFn('MyClass') //MyClass being the name of the class
I want to do this:
$obj->tempFn(MyClass) //Directly references the class name, instead of a string representation
No. But you can define a constant in your class, that contains the class name, like:
class foo{
const
NAME = 'foo';
}
And access it like foo::NAME.
In PHP 5.5, you'll be able to use:
foo::class
echo get_class($this);should work inside of a class.
echo __CLASS__; I believe this is a static property
If really wanting to avoid the statics I think the Reflection class might work.
function getClassName(ReflectionParameter $param) {
preg_match('/\[\s\<\w+?>\s([\w]+)/s', $param->__toString(), $matches);
return isset($matches[1]) ? $matches[1] : null;
}
That's from the comments on http://www.php.net/manual/en/reflectionparameter.getclass.php
I'm learned php as functional and procedure language. Right now try to start learn objective-oriented and got an important question.
I have code:
class car {
function set_car($model) {
$this->model = $model;
}
function check_model()
{
if($this->model == "Mercedes") echo "Good car";
}
}
$mycar = new car;
$mycar->set_car("Mercedes");
echo $mycar->check_model();
Why it does work without declaration of $model?
var $model; in the begin?
Because in php works "auto-declaration" for any variables?
I'm stuck
Every object in PHP can get members w/o declaring them:
$mycar = new car;
$mycar->model = "Mercedes";
echo $mycar->check_model(); # Good car
That's PHP's default behaviour. Those are public. See manual.
Yes, if it doesn't exist, PHP declares it on the fly for you.
It is more elegant to define it anyway, and when working with extends it's recommended, because you can get weird situations if your extends are gonna use the same varnames and also don't define it private, protected or public.
More info:
http://www.php.net/manual/en/language.oop5.visibility.php
PHP class members can be created at any time. In this way it will be treated as public variable. To declare a private variable you need to declare it.
Yes. But this way variables will be public. And declaration class variable as "var" is deprecated - use public, protected or private.
No, it's because $model is an argument of the function set_car. Arguments are not exactly variables, but placeholders (references) to the variables or values that will be set when calling the function (or class method). E.g., $model takes the value "Mercedes" when calling set_car.
I think this behavior can lead to errors.
Lets consider this code with one misprint
declare(strict_types=1);
class A
{
public float $sum;
public function calcSum(float $a, float $b): float
{
$this->sum = $a;
$this->sums = $a + $b; //misprinted sums instead of sum
return $this->sum;
}
}
echo (new A())->calcSum(1, 1); //prints 1
Even I use PHP 7.4+ type hints and so one, neither compiler, nor IDE with code checkers can't find this typo.
I have a string containing the class name and I wish to get a constant and call a (static) method from that class.
<?php
$myclass = 'b'; // My class I wish to use
$x = new x($myclass); // Create an instance of x
$response = $x->runMethod(); // Call "runMethod" which calls my desired method
// This is my class I use to access the other classes
class x {
private $myclass = NULL;
public function __construct ( $myclass ) {
if(is_string($myclass)) {
// Assuming the input has a valid class name
$this->myclass = $myclass;
}
}
public function runMethod() {
// Get the selected constant here
print $this->myclass::CONSTANT;
// Call the selected method here
return $this->myclass::method('input string');
}
}
// These are my class(es) I want to access
abstract class a {
const CONSTANT = 'this is my constant';
public static function method ( $str ) {
return $str;
}
}
class b extends a {
const CONSTANT = 'this is my new constant';
public static function method ( $str ) {
return 'this is my method, and this is my string: '. $str;
}
}
?>
As I expected (more or less), using $variable::CONSTANT or $variable::method(); doesn't work.
Before asking what I have tried; I've tried so many things I basically forgot.
What's the best approach to do this? Thanks in advance.
To access the constant, use constant():
constant( $this->myClass.'::CONSTANT' );
Be advised: If you are working with namespaces, you need to specifically add your namespace to the string even if you call constant() from the same namespace!
For the call, you'll have to use call_user_func():
call_user_func( array( $this->myclass, 'method' ) );
However: this is all not very efficient, so you might want to take another look at your object hierarchy design. There might be a better way to achieve the desired result, using inheritance etc.
in php 7 you can use this code
echo 'my class name'::$b;
or
#Uncomment this lines if you're the input($className and $constName) is safe.
$reg = '/^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$/';
if(preg_match($reg,$className) !== 1 || preg_match($reg,$constName) !== 1)
throw new \Exception('Oh, is it an attack?');
$value = eval("return $className::$constName;");
You can achieve it by setting a temporary variable. Not the most elegant way but it works.
public function runMethod() {
// Temporary variable
$myclass = $this->myclass;
// Get the selected constant here
print $myclass::CONSTANT;
// Call the selected method here
return $myclass::method('input string');
}
I guess it's to do with the ambiguity of the ::, at least that what the error message is hinting at (PHP Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM)
Use call_user_func to call static method:
call_user_func(array($className, $methodName), $parameter);
Classes defined as abstract may not be instantiated, and any class that contains at least one abstract method must also be abstract. Methods defined as abstract simply declare the method's signature - they cannot define the implementation.
When inheriting from an abstract class, all methods marked abstract in the parent's class declaration must be defined by the child; additionally, these methods must be defined with the same (or a less restricted) visibility. For example, if the abstract method is defined as protected, the function implementation must be defined as either protected or public, but not private. Furthermore the signatures of the methods must match, i.e. the type hints and the number of required arguments must be the same. This also applies to constructors as of PHP 5.4. Before 5.4 constructor signatures could differ.
Refer to http://php.net/manual/en/language.oop5.abstract.php
This might just be tangential to the subject but, while searching for my own issue I found that the accepted answer pointed me in the right direction, so I wanted to share my problem & solution in case someone else might be stuck in a similar fashion.
I was using the PDO class and was building some error options from an ini config file. I needed them in an associative array in the form: PDO::OPTION_KEY => PDO::OPTION_VALUE, but it was of course failing because I was trying to build the array with just PDO::$key => PDO::$value.
The solution (inspired from the accepted answer):
$config['options'] += [constant('PDO::'.$key) => constant('PDO::'.$option)];
where everything works if you concatenate the class name and the Scope Resolution Operator as a string with the variable and get the constant value of the resulting string through the constant function (more here).
Thank you and I hope this helps someone else!