PHP 8.1.15 Released!

简介

Every single expression in PHP has one of the following built-in types depending on its value:

  • null
  • bool
  • int
  • float (浮点数)
  • string
  • array
  • object
  • callable
  • resource

PHP is a dynamically typed language, which means that by default there is no need to specify the type of a variable, as this will be determined at runtime. However, it is possible to statically type some aspect of the language via the use of type declarations.

Types restrict the kind of operations that can be performed on them. However, if an expression/variable is used in an operation which its type does not support, PHP will attempt to type juggle the value into a type that supports the operation. This process depends on the context in which the value is used. For more information, see the section on Type Juggling.

小技巧

The type comparison tables may also be useful, as various examples of comparison between values of different types are present.

注意: It is possible to force an expression to be evaluated to a certain type by using a type cast. A variable can also be type cast in-place by using the settype() function on it.

To check the value and type of an expression, use the var_dump() function. To retrieve the type of an expression, use the get_debug_type() function. However, to check if an expression is of a certain type use the is_type functions instead.

$a_bool = true; // a bool
$a_str = "foo"; // a string
$a_str2 = 'foo'; // a string
$an_int = 12; // an int
echo get_debug_type($a_bool), "\n";
echo get_debug_type($a_str), "\n";

// 如果是整型,就加上 4
if (is_int($an_int)) {
$an_int += 4;
}
var_dump($an_int);

// 如果 $a_bool 是字符串,就打印出来
if (is_string($a_bool)) {
echo "String: $a_bool";
}
?>

以上例程在 PHP 8 中的输出:

bool
string
int(16)

注意: Prior to PHP 8.0.0, where the get_debug_type() is not available, the gettype() function can be used instead. However, it doesn't use the canonical type names.

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