What s the difference between double colon and - arrow in PHP

Question

There are two distinct ways to access methods in PHP  but what s the difference    response- gt setParameter  foo    bar      and  sfConfig  set  foo    bar      I m assuming - gt   dash with greater than sign or chevron  is used for functions for variables  and     double colons  is used for functions for classes  Correct   Is the   gt  assignment operator only used to assign data within an array   Is this in contrast to the   assignment operator which is used to instantiate or modify a variable

User · Answer

The difference between static and instantiated methods and properties seem to be one of the biggest obstacles to those just starting out with OOP PHP in PHP 5.

The double colon operator (which is called the Paamayim Nekudotayim from Hebrew - trivia) is used when calling an object or property from a static context. This means an instance of the object has not been created yet.

The arrow operator, conversely, calls methods or properties that from a reference of an instance of the object.

Static methods can be especially useful in object models that are linked to a database for create and delete methods, since you can set the return value to the inserted table id and then use the constructor to instantiate the object by the row id.

User · Answer

is used in static context  ie  when some method or property is declared as static   class Math       public static function sin  angle            return                result   Math  sin 123     Also  the    operator  the Scope Resolution Operator  a k a Paamayim Nekudotayim  is used in dynamic context when you invoke a method property of a parent class   class Rectangle        protected  x   y        public function   construct  x   y              this- gt x    x            this- gt y    y            class Square extends Rectangle       public function   construct  x            parent    construct  x   x             - gt  is used in dynamic context  ie  when you deal with some instance of some class   class Hello       public function say            echo  hello              h   new Hello     h- gt say      By the way  I don t think that using Symfony is a good idea when you don t have any OOP experience

User · Answer

Actually by this symbol we can call a class method that is static and not be dependent on other initialization     class Test        public  name       public function   construct              this- gt name    Mrinmoy Ghoshal              public static function doWrite  name            print  Hello    name             public function write             print  this- gt name            Here the doWrite   function is not dependent on any other method or variable  and it is a static method  That s why we can call this method by this operator without initializing the object of this class   Test  doWrite  Mrinmoy          Output  Hello Mrinmoy   But if you want to call the write method in this way  it will generate an error because it is dependent on initialization

User · Answer

When the left part is an object instance  you use - gt   Otherwise  you use      This means that - gt  is mostly used to access instance members  though it can also be used to access static members  such usage is discouraged   while    is usually used to access static members  though in a few special cases  it s used to access instance members    In general     is used for scope resolution  and it may have either a class name  parent  self  or  in PHP 5 3  static to its left  parent refers to the scope of the superclass of the class where it s used  self refers to the scope of the class where it s used  static refers to the  called scope   see late static bindings    The rule is that a call with    is an instance call if and only if    the target method is not declared as static and there is a compatible object context at the time of the call  meaning these must be true    the call is made from a context where  this exists and the class of  this is either the class of the method being called or a subclass of it     Example   class A       public function func instance             echo  in      METHOD      n             public function callDynamic             echo  in      METHOD      n           B  dyn              class B extends A       public static  prop static    B   prop static value       public  prop instance    B   prop instance value        public function func instance             echo  in      METHOD      n              this is one exception where    is required to access an            instance member             The super implementation of func instance is being            accessed here            parent  func instance            A  func instance      same as the statement above            public static function func static             echo  in      METHOD      n              public function   call  name   arguments            echo  in dynamic  name    call      n              public static function   callStatic  name   arguments            echo  in dynamic  name    callStatic      n             echo  B   prop static     B   prop static    n   echo  B  func static       B  func static      n    a   new A   b   new B  echo   b- gt prop instance      b- gt prop instance    n     not recommended  static method called as instance method   echo   b- gt func static        b- gt func static      n    echo   b- gt func instance        n    b- gt func instance      n       This is more tricky    in the first case  a static call is made because  this is an    instance of A  so B  dyn   is a method of an incompatible class     echo   a- gt dyn        n    a- gt callDynamic      n      in this case  an instance call is made because  this is an    instance of B  despite the fact we are in a method of A   so    B  dyn   is a method of a compatible class  namely  it s the    same class as the object s      echo   b- gt dyn        n    b- gt callDynamic      n     Output    B   prop static  B   prop static value B  func static    in B  func static   b- prop instance  B   prop instance value  b- func static    in B  func static   b- func instance    in B  func instance in A  func instance in A  func instance   a- dyn    in A  callDynamic in dynamic dyn    callStatic    b- dyn    in A  callDynamic in dynamic dyn    call

User · Answer

Yes  I just hit my first  PHP Parse error   syntax error  unexpected T PAAMAYIM NEKUDOTAYIM   My bad  I had a  instance  method   that should have been  instance- gt method    Silly me    The odd thing is that this still works just fine on my local machine  running PHP 5 3 8  - nothing  not even a warning with error reporting   E ALL - but not at all on the test server  there it just explodes with a syntax error and a white screen in the browser  Since PHP logging was turned off at the test machine  and the hosting company was too busy to turn it on  it was not too obvious    So  word of warning  apparently  some PHP installations will let you use a  instance  method    while others don t    If anybody can expand on why that is  please do

User · Answer

The   gt  operator is used to assign key-value pairs in an associative array  For example    fruits   array     Apple     gt   Red      Banana    gt   Yellow       It s meaning is similar in the foreach statement   foreach   fruits as  fruit   gt   color    echo   fruit is  color in color

[php] What's the difference between :: (double colon) and -> (arrow) in PHP?

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