starting use oop
why:
class user
{
private $pdo;
function __construct()
{
$this->pdo = singleton::get_instance()->PDO_connection();
}
...
}
this works fine. but this:
class user
{
private $pdo = singleton::get_instance()->PDO_connection();
...
}
this does not working. Error parse error, expecting ','' or ';'' in ...
what is wrong with second variant?
See the last sentence of the first paragraph of Properties in the PHP OOP documentation:
Class member variables are called
"properties". You may also see them
referred to using other terms such as
"attributes" or "fields", but for the
purposes of this reference we will use
"properties". They are defined by
using one of the keywords public,
protected, or private, followed by a
normal variable declaration. This
declaration may include an
initialization, but this
initialization must be a constant
value--that is, it must be able to be
evaluated at compile time and must not
depend on run-time information in
order to be evaluated.
In other words, the database handler returned by this statement is not a constant value and therefore will not be available at compile time:
singleton::get_instance()->PDO_connection();
Class properties cannot be assigned at declaration using functions. Scalar values, constants (though not constants of the current class), and arrays only.
Related
trait Foo {
private $url = config('api.url');
}
I have a url data set inside of config, however I need to put this value into trait's property. But it's not working. anyone know how to solve this problem?
what I did now is put construct inside of trait
public function __construct(){
$this->url = config('api.url');
}
it's not about traits, it's about php OOP nature itself:
here is the docs:
Class member variables are called "properties". You may also see them
referred to using other terms such as "attributes" or "fields", but
for the purposes of this reference we will use "properties". They are
defined by using one of the keywords public, protected, or private,
followed by a normal variable declaration. This declaration may
include an initialization, but this initialization must be a constant
value--that is, it must be able to be evaluated at compile time and
must not depend on run-time information in order to be evaluated.
from the docs example:
// invalid property declarations:
public $var4 = self::myStaticMethod();
public $var5 = $myVar;
I have a very simple issue where I am trying to set a private static property value made up of a constant appended with some text like this:
private static $cssDirectory = APP_ROOT.'css/';
I am getting a syntax error. I can fix this by making the private variable not static and assign a value with a constructor for example but since I want it static I am curious what can I do about it. I can also make a constant for the whole value and use that but again I am curious why I can't do it like I tried. Maybe I am doing something wrong also. Thanks.
From the PHP docs
Class member variables are called "properties"... They are defined by using one of the keywords public, protected, or private, followed by a normal variable declaration. This declaration may include an initialization, but this initialization must be a constant value --that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.
Concatenation is a run-time operation.
You don't need to instantiate and set the property value in the constructor.... you can write a static setter method instead
Note also that PHP 5.6 does allow this type of initialization of class properties
EDIT
Example of a static setter method:
private static $cssDirectory;
public static setCssDirectory() {
self::$cssDirectory = APP_ROOT.'css/';
}
And then you just call
myClassName::setCssDirectory();
before anything else
Why is not possible to initialize a property to a function when you declare the property in php? The following snippit results in a Parse error: syntax error, unexpected T_FUNCTION
<?php
class AssignAnonFunction {
private $someFunc = function() {
echo "Will Not work";
};
}
?>
Yet you can initialize a property to a string, number or other data types?
Edit:
But I can assign a function to a property in the __construct() method. The following does work:
<?php
class AssignAnonFunctionInConstructor {
private $someFunc;
public function __construct() {
$this->someFunc = function() {
echo "Does Work";
};
}
}
?>
Because it is not implemented in PHP.
http://www.php.net/manual/en/language.oop5.properties.php. Quote:
They (properties) are defined by using one of the
keywords public, protected, or
private, followed by a normal variable
declaration. This declaration may
include an initialization, but this
initialization must be a constant
value--that is, it must be able to be
evaluated at compile time and must not
depend on run-time information in
order to be evaluated.
You cannot initialize properties like this, functions are not constant values. Hence my original answer "it is not implemented".
Why is it not implemented? That I can only guess - it probably is quite a complex task and nobody has stepped up to implement it. And/or there may not be enough demand for a feature like that.
Closures do not exist in PHP until PHP 5.3 (the latest version). Make sure you have PHP 5.3 if you want to do this.
In earlier versions, you can sort of duplicate this functionality with the create_function() function, somewhat like this:
$someFunc = create_function($args,$code);
$someFunc();
Where $args is a string formatted like "$x,$y,$z" and $code is a string of your PHP code.
Here is my class
class Databases {
public $liveresellerdb = new Database('1host1','user','pswd','db');
}
the error i am getting is
Parse error: syntax error, unexpected T_NEW in /home/abhijitnair/sandbox/newreseller/Databases.php on line 33
why this error is coming?
Properties may not be preset with runtime information.
Quoting PHP Manual:
Class member variables are called "properties". You may also see them referred to using other terms such as "attributes" or "fields", but for the purposes of this reference we will use "properties". They are defined by using one of the keywords public, protected, or private, followed by a normal variable declaration. This declaration may include an initialization, but this initialization must be a constant value--that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.
<?php
class Databases {
public static $liveresellerdb;
}
Databases::$liveresellerdb = new Database('1host1','user','pswd','db');
?>
This is how you initialise a static member...
Because you forgot to write the static keyword to actually make the property static.
In addition, you can't initialise static properties with expressions like this. Here's a workaround.
you cannot assign object during the class preperation stages, only the class instantation:
class Databases
{
public $liveresellerdb;
public function __construct()
{
$this->liveresellerdb = new Database('1host1','user','pswd','db');
}
}
anything within the constructor can be generic PHP code, outside the function and instead the class body has specific laws.
if you require the database's to be static then you have to set / access them differently.
class Databases
{
public static $liveresellerdb;
}
Databases::liversellerdb = new Database('1host1','user','pswd','db');
Why is not possible to initialize a property to a function when you declare the property in php? The following snippit results in a Parse error: syntax error, unexpected T_FUNCTION
<?php
class AssignAnonFunction {
private $someFunc = function() {
echo "Will Not work";
};
}
?>
Yet you can initialize a property to a string, number or other data types?
Edit:
But I can assign a function to a property in the __construct() method. The following does work:
<?php
class AssignAnonFunctionInConstructor {
private $someFunc;
public function __construct() {
$this->someFunc = function() {
echo "Does Work";
};
}
}
?>
Because it is not implemented in PHP.
http://www.php.net/manual/en/language.oop5.properties.php. Quote:
They (properties) are defined by using one of the
keywords public, protected, or
private, followed by a normal variable
declaration. This declaration may
include an initialization, but this
initialization must be a constant
value--that is, it must be able to be
evaluated at compile time and must not
depend on run-time information in
order to be evaluated.
You cannot initialize properties like this, functions are not constant values. Hence my original answer "it is not implemented".
Why is it not implemented? That I can only guess - it probably is quite a complex task and nobody has stepped up to implement it. And/or there may not be enough demand for a feature like that.
Closures do not exist in PHP until PHP 5.3 (the latest version). Make sure you have PHP 5.3 if you want to do this.
In earlier versions, you can sort of duplicate this functionality with the create_function() function, somewhat like this:
$someFunc = create_function($args,$code);
$someFunc();
Where $args is a string formatted like "$x,$y,$z" and $code is a string of your PHP code.