PHP有關類的調用方式"->"與"::"的區別 · 學習筆記

**1.對非靜態屬性的調用** ~~~ class?Test?{ ????public?$commonProp??=?"a?commonProp"; } $test?=?new?Test(); var_dump($test->commonProp?);//正常:?"a?commonProp" var_dump($test->$commonProp?);//注意:未定義的變量&&致命:無法訪問空屬性 var_dump($test::commonProp?);//致命:未定義的類常量 var_dump($test::$commonProp?);//致命:訪問未聲明的靜態屬性 var_dump(Test->commonProp?);//解析錯誤,不受期待的"->" var_dump(Test->$commonProp?);//解析錯誤,不受期待的"->" var_dump(Test::commonProp?);//致命:未定義的類常量 var_dump(Test::$commonProp?);//致命:訪問未聲明的靜態屬性 exit; ~~~ **2.對靜態屬性的調用** ~~~ class?Test?{ ????public?static?$staticProp??=?"a?staticProp"; } $test?=?new?Test(); var_dump($test->staticProp?);//嚴格標準:對靜態屬性使用了非靜態的調用方式&&注意:未定義的屬性,?null var_dump($test->$staticProp?);//注意:未定義的變量&&致命:無法訪問空屬性 var_dump($test::staticProp?);//致命:未定義的類常量 var_dump($test::$staticProp?);//正常:?"a?staticProp" var_dump(Test->staticProp?);//解析錯誤,不受期待的"->" var_dump(Test->$staticProp?);//解析錯誤,不受期待的"->" var_dump(Test::staticProp?);//致命:未定義的類常量 var_dump(Test::$staticProp?);//正常:?"a?staticProp" exit; ~~~ **3.對類常量的調用** ~~~ class?Test?{ ????const?constant?=?"a?constant"?; } $test?=?new?Test(); var_dump($test->constant?);//注意:未定義的屬性,?null var_dump($test->$constant?);注意:未定義的變量&&致命:無法訪問空屬性 var_dump($test::constant?);//正常:?"a?constant" var_dump($test::$constant?);//致命:訪問未聲明的靜態屬性 var_dump(Test->constant?);//解析錯誤,不受期待的"->" var_dump(Test->$constant?);//解析錯誤,不受期待的"->" var_dump(Test::constant?);//正常:?"a?constant" var_dump(Test::$constant?);致命:訪問未聲明的靜態屬性 exit; ~~~ 4.對普通方法的調用 ~~~ class?Test?{ ????const?constant?=?"a?constant"?; ????public?$commonProp??=?'a?commonProp'; ????public?static?$staticProp=?'a?staticProp'; ????public?function?commonFunc(){ ????????//正常:?"$this->commonProp?=?a?commonProp" ????????echo?'$this->commonProp?=?'.$this->commonProp." "; ????????//注意:未定義的變量&&致命:無法訪問空屬性 ????????echo?'$this->$commonProp?=?'.$this->$commonProp." "; ????????//致命:未定義的類常量 ????????echo?'$this::commonProp?=?'.$this::commonProp." "; ????????//致命:訪問未聲明的靜態屬性 ????????echo?'$this::$commonProp?=?'.$this::$commonProp." "; ????????//解析錯誤,不受期待的"->" ????????echo?'self->commonProp?=?'.self->commonProp." "; ????????//解析錯誤,不受期待的"->" ????????echo?'self->$commonProp?=?'.self->$commonProp." "; ????????//致命:未定義的類常量 ????????echo?'self->commonProp?=?'.self->commonProp." "; ????????//致命:訪問未聲明的靜態屬性 ????????echo?'self->commonProp?=?'.self->commonProp." "; ???????????? ????????//嚴格標準:對靜態屬性使用了非靜態的調用方式&&注意:未定義的屬性,?"$this->staticProp?=?" ????????echo?'$this->staticProp?=?'.$this->staticProp." "; ????????//注意:未定義的變量&&致命:無法訪問空屬性 ????????echo?'$this->$staticProp?=?'.$this->$staticProp." "; ????????//致命:未定義的類常量 ????????echo?'$this::staticProp?=?'.$this::staticProp." "; ????????//正常:"$this::$staticProp?=?a?staticProp" ????????echo?'$this::$staticProp?=?'.$this::$staticProp." "; ????????//解析錯誤,不受期待的"->" ????????echo?'self->staticProp?=?'.self->staticProp." "; ????????//解析錯誤,不受期待的"->" ????????echo?'self->$staticProp?=?'.self->$staticProp." "; ????????//致命:未定義的類常量 ????????echo?'self::staticProp?=?'.self::staticProp." "; ????????//正常:"self::$staticProp?=?a?staticProp" ????????echo?'self::$staticProp?=?'.self::$staticProp." "; ?????????????? ????????//注意:未定義的屬性,"$this->constant?=?" ????????echo?'$this->constant?=?'.$this->constant." "; ????????//注意:未定義的變量&&致命:無法訪問空屬性 ????????echo?'$this->$constant?=?'.$this->$constant." "; ????????//正常:$this::constant?=?a?constant ????????echo?'$this::constant?=?'.$this::constant." "; ????????//致命:訪問未聲明的靜態屬性 ????????echo?'$this::$constant?=?'.$this::$constant." "; ????????//解析錯誤,不受期待的"->" ????????echo?'self->constant?=?'.self->constant." "; ????????//解析錯誤,不受期待的"->" ????????echo?'self->$constant?=?'.self->$constant." "; ????????//正常:"self::constant?=?a?constant" ????????echo?'self::constant?=?'.self::constant." "; ????????//致命:訪問未聲明的靜態屬性 ????????echo?'self::$constant?=?'.self::$constant." "; ????} } $test?=?new?Test(); $test->commonFunc(); $test::commonFunc();//嚴格標準:非靜態方法不能被靜態調用 Test>commonFunc();//解析錯誤,不受期待的"->" Tes::commonFunc();//非靜態方法不能被靜態調用 ~~~ 5.對靜態方法的調用 ~~~ class?Test?{ ????const?constant?=?"a?constant"?; ????public?$commonProp??=?'a?commonProp'; ????public?static?$staticProp=?'a?staticProp'; ????public?static?function?staticFunc(){ ??????//致命:在非對象語境[靜態方法內]下使用了$this ??????echo?'$this->commonProp?=?'.$this->commonProp." "; ??????//致命:在非對象語境[靜態方法內]下使用了$this ??????echo?'$this->$commonProp?=?'.$this->$commonProp." "; ??????//警告:未定義的變量$this?&&?致命:類名應該是字符串或者對象變量 ??????echo?'$this::commonProp?=?'.$this::commonProp." "; ??????//警告:未定義的變量$this?&&?致命:類名應該是字符串或者對象變量 ??????echo?'$this::$commonProp?=?'.$this::$commonProp." "; ??????//解析錯誤,不受期待的"->" ??????echo?'self->commonProp?=?'.self->commonProp." "; ??????//解析錯誤,不受期待的"->" ??????echo?'self->$commonProp?=?'.self->$commonProp." "; ??????//致命:未定義的類常量 ??????echo?'self::commonProp?=?'.self::commonProp." "; ??????//致命:訪問未聲明的靜態屬性 ??????echo?'self::$commonProp?=?'.self::$commonProp." "; ???????? ??????//致命:在非對象語境[靜態方法內]下使用了$this ??????echo?'$this->staticProp?=?'.$this->staticProp." "; ??????//致命:在非對象語境[靜態方法內]下使用了$this ??????echo?'$this->$staticProp?=?'.$this->$staticProp." "; ??????//警告:未定義的變量$this?&&?致命:類名應該是字符串或者對象變量 ??????echo?'$this::staticProp?=?'.$this::staticProp." "; ??????//警告:未定義的變量$this?&&?致命:類名應該是字符串或者對象變量 ??????echo?'$this::$staticProp?=?'.$this::$staticProp." "; ??????//解析錯誤,不受期待的"->" ??????echo?'self->staticProp?=?'.self->staticProp." "; ??????//解析錯誤,不受期待的"->" ??????echo?'self->$staticProp?=?'.self->$staticProp." "; ??????//致命:未定義的類常量 ??????echo?'self::staticProp?=?'.self::staticProp." "; ??????//正常:"self::$staticProp?=?a?staticProp" ??????echo?'self::$staticProp?=?'.self::$staticProp." "; ????????????? ??????//注意:未定義的屬性,"$this->constant?=?" ??????echo?'$this->constant?=?'.$this->constant." "; ??????//注意:未定義的變量&&致命:無法訪問空屬性 ??????echo?'$this->$constant?=?'.$this->$constant." "; ??????//正常:$this::constant?=?a?constant ??????echo?'$this::constant?=?'.$this::constant." "; ??????//致命:訪問未聲明的靜態屬性 ??????echo?'$this::$constant?=?'.$this::$constant." "; ??????//解析錯誤,不受期待的"->" ??????echo?'self->constant?=?'.self->constant." "; ??????//解析錯誤,不受期待的"->" ??????echo?'self->$constant?=?'.self->$constant." "; ??????//正常:"self::constant?=?a?constant" ??????echo?'self::constant?=?'.self::constant." "; ??????//致命:訪問未聲明的靜態屬性 ??????echo?'self::$constant?=?'.self::$constant." ";???????????????????????????????? ????} } $test?=?new?Test(); $test->staticFunc();//調用方式沒有報錯. $test::staticFunc();//調用方式沒有報錯 Test>staticFunc();//解析錯誤,不受期待的"->" Test::staticFunc();//調用方式沒有報錯 ~~~ 驗證結論: 1. 方法體內即使包含了對靜態屬性的調用,方法也不一定要聲明為靜態的 2. 如果方法沒有聲明為靜態的,則不能使用靜態的調用方式 3. 外部對象實例$instance->與類內部$this->有同樣的表現,外部class::與內部self::有同樣的表現 4. class和self不能使用調用符號-> 5. 對普通屬性的調用方式只能是 $instance($this)->屬性名 6. 對靜態屬性的調用必須使用靜態調用符號::且自身的表現形式一定要加$,但是對調用方沒有要求class\[self\]或$insance\[$this\]都可以 7. 對類常量的調用必須使用靜態調用符號::且自身的表現形式一定不能加$,但是對調用方沒有要求class\[self\]或$insance\[$this\]都可以 8. 靜態方法中不能使用$this,靜態方法在類加載的時候就加載進內存，此時$this的對象還沒有生成,所以會報錯總結 1. 靜態方法里不能出現$this\[對象實例引用\],非靜態方法沒有任何限制,可以有$this->|$this::|self:: 2. "->"僅限于實例使用,僅限于調用常規屬性和方法上 3. "::"不僅類可以使用,實例也可以使用,但僅限于調用類常量,靜態屬性和方法上