trait_exists

Function name: trait_exists()

Function function: determines whether the specified trait has been defined

Applicable version: PHP 5 >= 5.4.0, PHP 7

Syntax: bool trait_exists ( string $traitname [, bool $autoload = true ] )

parameter:

• $traitname: The trait name, string type to check.
• $autoload: Optional parameter, specifying whether the missing trait is automatically loaded, default is true. If set to false, false will be returned when trait does not exist.

Return value: Return true if trait is defined, otherwise false.

Example:

 trait MyTrait { public function myMethod() { echo "This is a method defined in MyTrait."; } } // 检查trait是否已定义if (trait_exists('MyTrait')) { echo "MyTrait is defined."; } else { echo "MyTrait is not defined."; } // 输出：MyTrait is defined.

 // 未定义MyTrait if (trait_exists('NonExistentTrait')) { echo "NonExistentTrait is defined."; } else { echo "NonExistentTrait is not defined."; } // 输出：NonExistentTrait is not defined.

 // 关闭自动加载if (trait_exists('AnotherTrait', false)) { echo "AnotherTrait is defined."; } else { echo "AnotherTrait is not defined."; } // 输出：AnotherTrait is not defined.

Notes:

• When trait does not exist, if the $autoload parameter is set to true (the default value), the trait_exists() function will try to automatically load the missing trait. If the automatic load fails, the function returns false.
• If trait has been loaded in other ways, the trait_exists() function will return true and will not be loaded again.
• In versions prior to PHP 5.4.0, the trait_exists() function is not available.
• The trait_exists() function can be used to check whether the trait is defined to avoid repeated errors in defining trait.
• The trait_exists() function can also be used to check whether a trait needs to be loaded, thereby avoiding duplicate loading.