PHP 关键字

PHP 有一组关键字是保留字，不能用作函数名、类名或方法名。在 PHP 7 之前，这些关键字也不能用作类属性名称：

Keyword	Description
abstract	Declare a class as abstract
and	A logical operator
as	Used in the foreach loop
break	Break out of loops and switch statements
callable	A data type which can be executed as a function
case	Used in the switch conditional
catch	Used in the try..catch statement
class	Declare a class
clone	Create a copy of an object
const	Define a class constant
continue	Jump to the next iteration of a loop
declare	Set directives for a block of code
default	Used in the switch statement
do	Create a do...while loop
echo	Output text
else	Used in conditional statements
elseif	Used in conditional statements
empty	Check if an expression is empty
enddeclare	End a declare block
endfor	End a for block
endforeach	End a foreach block
endif	End an if or elseif block
endswitch	End a switch block
endwhile	End a while block
extends	Extends a class or interface
final	Declare a class, property or method as final
finally	Used in the try...catch statement
fn	Declare an arrow function
for	Create a for loop
foreach	Create a foreach loop
function	Create a function
global	Import variables from the global scope
goto	Jump to a line of code
if	Create a conditional statement
implements	Implement an interface
include	Embed code from another file
include_once	Embed code from another file
instanceof	Test an object's class
insteadof	Resolve conflicts with traits
interface	Declare an interface
isset	Check if a variable exists and is not null
list	Assigns array elements into variables
namespace	Declares a namespace
new	Creates an object
or	A logical operator
print	Output text
private	Declare a property, method or constant as private
protected	Declare a property, method or constant as protected
public	Declare a property, method or constant as public
require	Embed code from another file
require_once	Embed code from another file
return	Exit a function and return a value
static	Declare a property or method as static
switch	Create a switch block
throw	Throw an exception
trait	Declare a trait
try	Create a try...catch structure
unset	Delete a variable or array element
use	Use a namespace
var	Declare a variable
while	Create a while loop or end a do...while loop
xor	A logical operator
yield	Used in generator functions
yield from	Used in generator functions