Тип var в php
Variables in PHP are represented by a dollar sign followed by the name of the variable. The variable name is case-sensitive.
Variable names follow the same rules as other labels in PHP. A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: ^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$
Note: For our purposes here, a letter is a-z, A-Z, and the bytes from 128 through 255 ( 0x80-0xff ).
Note: $this is a special variable that can’t be assigned. Prior to PHP 7.1.0, indirect assignment (e.g. by using variable variables) was possible.
For information on variable related functions, see the Variable Functions Reference.
$var = ‘Bob’ ;
$Var = ‘Joe’ ;
echo » $var , $Var » ; // outputs «Bob, Joe»
$ 4site = ‘not yet’ ; // invalid; starts with a number
$_4site = ‘not yet’ ; // valid; starts with an underscore
$täyte = ‘mansikka’ ; // valid; ‘ä’ is (Extended) ASCII 228.
?>
By default, variables are always assigned by value. That is to say, when you assign an expression to a variable, the entire value of the original expression is copied into the destination variable. This means, for instance, that after assigning one variable’s value to another, changing one of those variables will have no effect on the other. For more information on this kind of assignment, see the chapter on Expressions.
PHP also offers another way to assign values to variables: assign by reference. This means that the new variable simply references (in other words, «becomes an alias for» or «points to») the original variable. Changes to the new variable affect the original, and vice versa.
To assign by reference, simply prepend an ampersand (&) to the beginning of the variable which is being assigned (the source variable). For instance, the following code snippet outputs ‘ My name is Bob ‘ twice:
$foo = ‘Bob’ ; // Assign the value ‘Bob’ to $foo
$bar = & $foo ; // Reference $foo via $bar.
$bar = «My name is $bar » ; // Alter $bar.
echo $bar ;
echo $foo ; // $foo is altered too.
?>
One important thing to note is that only named variables may be assigned by reference.
$foo = 25 ;
$bar = & $foo ; // This is a valid assignment.
$bar = &( 24 * 7 ); // Invalid; references an unnamed expression.
It is not necessary to initialize variables in PHP however it is a very good practice. Uninitialized variables have a default value of their type depending on the context in which they are used — booleans default to false , integers and floats default to zero, strings (e.g. used in echo ) are set as an empty string and arrays become to an empty array.
Example #1 Default values of uninitialized variables
// Unset AND unreferenced (no use context) variable; outputs NULL
var_dump ( $unset_var );
// Boolean usage; outputs ‘false’ (See ternary operators for more on this syntax)
echo $unset_bool ? «true\n» : «false\n» ;
// String usage; outputs ‘string(3) «abc»‘
$unset_str .= ‘abc’ ;
var_dump ( $unset_str );
// Integer usage; outputs ‘int(25)’
$unset_int += 25 ; // 0 + 25 => 25
var_dump ( $unset_int );
// Float usage; outputs ‘float(1.25)’
$unset_float += 1.25 ;
var_dump ( $unset_float );
// Array usage; outputs array(1) < [3]=>string(3) «def» >
$unset_arr [ 3 ] = «def» ; // array() + array(3 => «def») => array(3 => «def»)
var_dump ( $unset_arr );
// Object usage; creates new stdClass object (see http://www.php.net/manual/en/reserved.classes.php)
// Outputs: object(stdClass)#1 (1) < ["foo"]=>string(3) «bar» >
$unset_obj -> foo = ‘bar’ ;
var_dump ( $unset_obj );
?>
Relying on the default value of an uninitialized variable is problematic in the case of including one file into another which uses the same variable name. E_WARNING (prior to PHP 8.0.0, E_NOTICE ) level error is issued in case of working with uninitialized variables, however not in the case of appending elements to the uninitialized array. isset() language construct can be used to detect if a variable has been already initialized.
User Contributed Notes 5 notes
This page should include a note on variable lifecycle:
Before a variable is used, it has no existence. It is unset. It is possible to check if a variable doesn’t exist by using isset(). This returns true provided the variable exists and isn’t set to null. With the exception of null, the value a variable holds plays no part in determining whether a variable is set.
Setting an existing variable to null is a way of unsetting a variable. Another way is variables may be destroyed by using the unset() construct.
print isset( $a ); // $a is not set. Prints false. (Or more accurately prints ».)
$b = 0 ; // isset($b) returns true (or more accurately ‘1’)
$c = array(); // isset($c) returns true
$b = null ; // Now isset($b) returns false;
unset( $c ); // Now isset($c) returns false;
?>
is_null() is an equivalent test to checking that isset() is false.
The first time that a variable is used in a scope, it’s automatically created. After this isset is true. At the point at which it is created it also receives a type according to the context.
$a_bool = true ; // a boolean
$a_str = ‘foo’ ; // a string
?>
If it is used without having been given a value then it is uninitalized and it receives the default value for the type. The default values are the _empty_ values. E.g Booleans default to FALSE, integers and floats default to zero, strings to the empty string », arrays to the empty array.
A variable can be tested for emptiness using empty();
$a = 0 ; //This isset, but is empty
?>
Unset variables are also empty.
empty( $vessel ); // returns true. Also $vessel is unset.
?>
Everything above applies to array elements too.
$item = array();
//Now isset($item) returns true. But isset($item[‘unicorn’]) is false.
//empty($item) is true, and so is empty($item[‘unicorn’]
$item [ ‘unicorn’ ] = » ;
//Now isset($item[‘unicorn’]) is true. And empty($item) is false.
//But empty($item[‘unicorn’]) is still true;
$item [ ‘unicorn’ ] = ‘Pink unicorn’ ;
//isset($item[‘unicorn’]) is still true. And empty($item) is still false.
//But now empty($item[‘unicorn’]) is false;
?>
For arrays, this is important because accessing a non-existent array item can trigger errors; you may want to test arrays and array items for existence with isset before using them.
Тип var в php
While waiting for native support for typed arrays, here are a couple of alternative ways to ensure strong typing of arrays by abusing variadic functions. The performance of these methods is a mystery to the writer and so the responsibility of benchmarking them falls unto the reader.
PHP 5.6 added the splat operator (. ) which is used to unpack arrays to be used as function arguments. PHP 7.0 added scalar type hints. Latter versions of PHP have further improved the type system. With these additions and improvements, it is possible to have a decent support for typed arrays.
function typeArrayNullInt (? int . $arg ): void >
function doSomething (array $ints ): void (function (? int . $arg ) <>)(. $ints );
// Alternatively,
( fn (? int . $arg ) => $arg )(. $ints );
// Or to avoid cluttering memory with too many closures
typeArrayNullInt (. $ints );
function doSomethingElse (? int . $ints ): void /* . */
>
$ints = [ 1 , 2 , 3 , 4 , null ];
doSomething ( $ints );
doSomethingElse (. $ints );
?>
Both methods work with all type declarations. The key idea here is to have the functions throw a runtime error if they encounter a typing violation. The typing method used in doSomethingElse is cleaner of the two but it disallows having any other parameters after the variadic parameter. It also requires the call site to be aware of this typing implementation and unpack the array. The method used in doSomething is messier but it does not require the call site to be aware of the typing method as the unpacking is performed within the function. It is also less ambiguous as the doSomethingElse would also accept n individual parameters where as doSomething only accepts an array. doSomething’s method is also easier to strip away if native typed array support is ever added to PHP. Both of these methods only work for input parameters. An array return value type check would need to take place at the call site.
If strict_types is not enabled, it may be desirable to return the coerced scalar values from the type check function (e.g. floats and strings become integers) to ensure proper typing.
same data type and same value but first function declare as a argument type declaration and return int(7)
and second fucntion declare as a return type declaration but return int(8).
function argument_type_declaration(int $a, int $b) return $a+$b;
>
function return_type_declaration($a,$b) :int return $a+$b;
>
Что делает ключевое слово PHP «var»?
Это, наверное, очень тривиальный вопрос, но я не смог найти ответ ни через поисковые системы, ни на php.net. Пожалуйста, просто направьте меня туда, где я могу прочитать об этом, если у вас нет времени объяснять.
Это для объявления переменных класса класса в PHP4 и больше не требуется. Он будет работать в PHP5, но повысит предупреждение E_STRICT в PHP с версии 5.0.0 до версии 5.1.2, когда он устарел. Начиная с PHP 5.3, var был устаревшим и является синонимом «public».
Ключевое слово var используется для объявления переменных в классе в PHP 4 :
С введением свойства свойства и метода PHP 5 был введен ( public , protected и private ), и поэтому var устарел.
Примечание. Метод PHP 4 объявления переменной с ключевым словом var по-прежнему поддерживается по соображениям совместимости (в качестве синонима для открытого ключевого слова). В PHP 5 до 5.1.3 его использование генерирует предупреждение E_STRICT.
Ответ. Из php 5.3 и > ключевое слово var эквивалентно public при объявлении переменных внутри класса.
совпадает с (для php 5.3 и > ):
История. Ранее это было нормой для объявления переменных в классах, но позже обесценилось, но позже (PHP 5.3) она стала обесцененной.
Так что в основном это старый стиль и не использовать его для более новой версии PHP. Лучше использовать ключевое слово Public, если вы не любите ключевое слово var. Поэтому вместо использования
var используется как public .if varable объявляется следующим образом в классе var $ a; если это означает, что его область является общедоступной для класса. в простых словах var ~ public