Best way to do multiple constructors in PHP

Question

You can t put two   construct functions with unique argument signatures in a PHP class  I d like to do this   class Student       protected  id     protected  name        etc      public function   construct  id           this- gt id    id           other members are still uninitialized          public function   construct  row from database           this- gt id    row from database- gt id          this- gt name    row from database- gt name            etc           What is the best way to do this in PHP

User · Answer

I created this method to let use it not only on constructors but in methods:

My constructor:

function __construct() {
    $paramsNumber=func_num_args();
    if($paramsNumber==0){
        //do something
    }else{
        $this->overload('__construct',func_get_args());
    }
}

My doSomething method:

public function doSomething() {
    $paramsNumber=func_num_args();
    if($paramsNumber==0){
        //do something
    }else{
        $this->overload('doSomething',func_get_args());
    }
}

Both works with this simple method:

public function overloadMethod($methodName,$params){
    $paramsNumber=sizeof($params);
    //methodName1(), methodName2()...
    $methodNameNumber =$methodName.$paramsNumber;
    if (method_exists($this,$methodNameNumber)) {
        call_user_func_array(array($this,$methodNameNumber),$params);
    }
}

So you can declare

__construct1($arg1), __construct2($arg1,$arg2)...

or

methodName1($arg1), methodName2($arg1,$arg2)...

and so on :)

And when using:

$myObject =  new MyClass($arg1, $arg2,..., $argN);

it will call __constructN, where you defined N args

then $myObject -> doSomething($arg1, $arg2,..., $argM)

it will call doSomethingM, , where you defined M args;

User · Answer

public function   construct          parameters   func get args                o   new MyClass  One    Two   3     Now  paramters will be an array with the values  One    Two   3   Edit   I can add that   func num args     will give you the number of parameters to the function

User · Answer

Hmm  surprised I don t see this answer yet  suppose I ll throw my hat in the ring   class Action       const cancelable        0      const target            1     const type              2       public  cancelable      public  target      public  type          construct   opt                   this- gt cancelable     isset  opt cancelable      opt cancelable    true           this- gt target         isset  opt target          opt target    NULL           this- gt type           isset  opt type            opt type     action               myAction   new Action        Action  cancelable   gt  false      Action  type   gt   spin                           You can optionally separate the options into their own class  such as extending SplEnum   abstract class ActionOpt extends SplEnum      const cancelable        0      const target            1     const type              2

User · Answer

Call constructors by data type   class A         function   construct  argument                 type   gettype  argument           if  type     unknown type                           type unknown                   this- gt     construct    type   argument               function   construct boolean  argument                     do something           function   construct integer  argument                     do something           function   construct double  argument                     do something           function   construct string  argument                     do something           function   construct array  argument                     do something           function   construct object  argument                     do something           function   construct resource  argument                     do something               other functions

User · Answer

As has already been shown here  there are many ways of declaring multiple constructors in PHP  but none of them are the correct way of doing so  since PHP technically doesn t allow it   But it doesn t stop us from hacking this functionality    Here s another example    lt  php  class myClass       public function   construct              get arguments         func get args             number of arguments   func num args             if  method exists  this   method name      construct   number of arguments                 call user func array array  this   method name    get arguments                        public function   construct1  argument1            echo  constructor with 1 parameter      argument1     n              public function   construct2  argument1   argument2            echo  constructor with 2 parameter      argument1          argument2     n              public function   construct3  argument1   argument2   argument3            echo  constructor with 3 parameter      argument1          argument2          argument3     n             object1   new myClass  BUET     object2   new myClass  BUET    is     object3   new myClass  BUET    is    Best       Source  The easiest way to use and understand multiple constructors    Hope this helps

User · Answer

You could always add an extra parameter to the constructor called something like mode and then perform a switch statement on it     class myClass        var  error       function   construct    data   mode                  this- gt error   false         switch    mode                          id    processId    data     break                row    processRow    data    break               default    this- gt error   true   break                           function processId    data        code           function processRow    data        code          a   new myClass    data   id       b   new myClass    data   row       c   new myClass    data   something       if    a- gt error      exit    invalid mode      if    b- gt error      exit   invalid mode      if    c- gt error      exit   invalid mode        Also with that method at any time if you wanted to add more functionality you can just add another case to the switch statement  and you can also check to make sure someone has sent the right thing through - in the above example all the data is ok except for C as that is set to  something  and so the error flag in the class is set and control is returned back to the main program for it to decide what to do next  in the example I just told it to exit with an error message  invalid mode  - but alternatively you could loop it back round until valid data is found

User · Answer

I know I m super late to the party here  but I came up with a fairly flexible pattern that should allow some really interesting and versatile implementations   Set up your class as you normally would  with whatever variables you like     class MyClass      protected  myVar1      protected  myVar2       public function   construct  obj   null           if  obj               foreach    object  obj  as  key   gt   value                    if isset  value   amp  amp  in array  key  array keys get object vars  this                           this- gt  key    value                                                      When you make your object just pass an associative array with the keys of the array the same as the names of your vars  like so      sample variable   new MyClass        myVar2   gt 123        i dont want this one   gt   This won  t make it into the class           print r  sample variable     The print r  sample variable   after this instantiation yields the following   MyClass Object    myVar1 protected    gt   myVar2 protected    gt  123    Because we ve initialize  group to null in our   construct       it is also valid to pass nothing whatsoever into the constructor as well  like so       sample variable   new MyClass     print r  sample variable     Now the output is exactly as expected   MyClass Object    myVar1 protected    gt   myVar2 protected    gt     The reason I wrote this was so that I could directly pass the output of json decode      to my constructor  and not worry about it too much    This was executed in PHP 7 1   Enjoy

User · Answer

Another option is to use default arguments in the constructor like this  class Student        private  id      private  name                 public function   construct  id   row array               this- gt id    id          foreach  row as  key   gt   value   this- gt  key    value            This means you ll need to instantiate with a row like this   student   new Student  row  id     row  but keeps your constructor nice and clean   On the other hand  if you want to make use of polymorphism then you can create two classes like so   class Student        public function   construct  row             foreach  row as  key   gt   value   this- gt  key    value           class EmptyStudent extends Student        public function   construct  id            parent    construct array  id    gt   id

User · Answer

More modern aproach  You are mixing seperate classes into one  entity  amp  data hydration  So for your case you should have 2 classes  class Student       protected  id     protected  name        etc    class StudentHydrator      public function hydrate Student  student  array  data          student- gt setId  data  id           if isset  data  name              student- gt setName  data  name                      etc  Can be replaced with foreach       return  student            usage  hydrator   new StudentHydrator     student    hydrator- gt hydrate new Student      id   gt 4     student2    hydrator- gt hydrate new Student     rowFromDB    Also please note that you should use doctrine or other ORM that already provides automatic entity hydration  And you should use dependency injection in order to skip mannualy creating objects like StudentHydrator

User · Answer

The solution of Kris is really nice  but I prefer a mix of factory and fluent style   lt  php  class Student        protected  firstName      protected  lastName         etc                  Constructor             public function   construct                allocate your stuff                       Static constructor   factory             public static function create             return new self                          FirstName setter - fluent style             public function setFirstName  firstName             this- gt firstName    firstName          return  this                        LastName setter - fluent style             public function setLastName  lastName             this- gt lastName    lastName          return  this               create instance  student  Student  create  - gt setFirstName  quot John quot  - gt setLastName  quot Doe quot        see result var dump  student     gt

User · Answer

In response to the best answer by Kris  which amazingly helped design my own class btw   here is a modified version for those that might find it useful  Includes methods for selecting from any column and dumping object data from array  Cheers   public function   construct          this - gt  id   0               public static function Exists  id        if    id  return false       id    int  id      if   id  lt   0  return false       mysqli   Mysql  Connect        if  mysqli num rows mysqli query  mysqli   SELECT id FROM users WHERE id        id      1  return true      return false     public static function FromId  id         u   new self        if    u - gt  FillFromColumn  id    id   return false      return  u     public static function FromColumn  column   value         u   new self        if    u - gt  FillFromColumn  column   value   return false      return  u     public static function FromArray  row   array          if   is array  row      row    array    return false       u   new self         u - gt  FillFromArray  row       return  u     protected function FillFromColumn  column   value         mysqli   Mysql  Connect          Assuming we re only allowed to specified EXISTENT columns      result   mysqli query  mysqli   SELECT   FROM users WHERE      column             value              count   mysqli num rows  result       if   count    0  return false       row   mysqli fetch assoc  result        this - gt  FillFromArray  row      protected function FillFromArray array  row        foreach  row as  i   gt   v            if  isset  this - gt   i                  this - gt   i    v                     public function ToArray          m   array        foreach   this as  i   gt   v             m  i     v                return  m     public function Dump         print r   lt PRE gt         print r  this - gt  ToArray         print r   lt  PRE gt

User · Answer

Let me add my grain of sand here  I personally like adding a constructors as static functions that return an instance of the class  the object   The following code is an example    class Person         private  name       private  email        public static function withName  name                   person   new Person              person- gt name    name            return  person               public static function withEmail  email                   person   new Person              person- gt email    email            return  person              Note that now you can create instance of the Person class like this    person1   Person  withName  Example     person2   Person  withEmail  yo mi email com      I took that code from   http   alfonsojimenez com post 30377422731 multiple-constructors-in-php

User · Answer

This is my take on it  build for php 5 6     It will look at constructor parameter types  array  class name  no description  and compare the given arguments  Constructors must be given with least specificity last  With examples      demo class class X       public  X       public function   construct  x             this- gt X    x             public function   toString             return  X   this- gt X              demo class class Y       public  Y       public function   construct  y             this- gt Y    y            public function   toString             return  Y   this- gt Y              here be magic abstract class MultipleConstructors       function   construct                get arguments         func get args               number of arguments   func num args                reflect   new ReflectionClass  this           foreach    reflect- gt getMethods   as    reflectmethod                   method name      reflectmethod- gt getName                if  substr    method name  0  strlen    construct           construct                        parms      reflectmethod- gt getParameters                    if  count    parms        number of arguments                           argsFit   true                      foreach     parms as    argPos   gt     param                               paramClass     param- gt getClass                               argVar   func get arg    argPos                              argVarType   gettype    argVar                              paramIsArray      param- gt isArray      true                             argVarIsArray      argVarType     array                              parameter is array and argument isn t  or the other way around                          if      paramIsArray  amp  amp      argVarIsArray                                      paramIsArray  amp  amp     argVarIsArray                                    argsFit   false                              continue                                                       class check                         if    is null    paramClass   amp  amp     argVarType     object                                   is null    paramClass   amp  amp     argVarType     object                                    argsFit   false                              continue                                                    if   is null    paramClass   amp  amp     argVarType     object                                    class type check                                paramClassName    N A                               if     paramClass                                     paramClassName      paramClass- gt getName                                if     paramClassName    get class    argVar                                        argsFit   false                                                                                                    if     argsFit                            call user func array array  this     method name      get arguments                           return                                                                          throw new Exception  No matching constructors                how to use multiple constructors class A extends MultipleConstructors       public  value       function   constructB array  hey             this- gt value    Array   count  hey    lt br  gt              function   construct1 X  first             this- gt value    first    lt br  gt               function   construct2 Y  second             this- gt value    second    lt br  gt              function   constructA  hey             this- gt value    hey   lt br  gt               function   toString             return  this- gt value            x   new X  foo     y   new Y  bar      aa   new A array  one    two    three     echo  aa    ar   new A  baz    echo  ar    ax   new A  x   echo  ax    ay   new A  y   echo  ay    Result   Array 3 baz Xfoo Ybar   Instead of the terminating exception if no constructor is found  it could be remove and allow for  empty  constructor  Or whatever you like

User · Answer

Here is an elegant way to do it  Create trait that will enable multiple constructors given the number of parameters   You would simply add the number of parameters to the function name    construct    So one parameter will be    construct1   two    construct2     etc   trait constructable       public function   construct                    a   func get args              i   func num args             if  method exists  this  f    construct   i                  call user func array   this  f   a                         class a      use constructable       public  result       public function   construct1  a            this- gt result    a             public function   construct2  a   b            this- gt result     a    b           echo  new a 1  - gt result        1 echo  new a 1 2  - gt result      3

User · Answer

I d probably do something like this    lt  php  class Student       public function   construct                allocate your stuff            public static function withID   id              instance   new self             instance- gt loadByID   id            return  instance             public static function withRow  array  row              instance   new self             instance- gt fill   row            return  instance             protected function loadByID   id                do query          row   my awesome db access stuff   id             this- gt fill   row               protected function fill  array  row                fill all properties from array            gt    Then if i want a Student where i know the ID    student   Student  withID   id      Or if i have an array of the db row    student   Student  withRow   row      Technically you re not building multiple constructors  just static helper methods  but you get to avoid a lot of spaghetti code in the constructor this way

User · Answer

For php7  I compare parameters type as well  you can have two constructors with same number of parameters but different type   trait GenericConstructorOverloadTrait                   var array Constructors metadata             private static  constructorsCache                 Generic constructor        GenericConstructorOverloadTrait constructor              public function   construct                  params   func get args             numParams   func num args              finish   false           if  self   constructorsCache                class   new  ReflectionClass  this                constructors    array filter  class- gt getMethods                    function   ReflectionMethod  method                    return preg match       construct 0-9      method- gt getName                                 self   constructorsCache    constructors                    else               constructors   self   constructorsCache                    foreach  constructors as  constructor                reflectionParams    constructor- gt getParameters                if count  reflectionParams      numParams                   continue                             matched   true              for  i 0   i lt   numParams   i                     if  reflectionParams  i - gt hasType                          type    reflectionParams  i - gt getType  - gt   toString                                      if                                                   reflectionParams  i - gt hasType                                reflectionParams  i - gt hasType    amp  amp                              is object  params  i    amp  amp                               params  i  instanceof  type                               reflectionParams  i - gt hasType    amp  amp                               reflectionParams  i - gt getType  - gt   toString                                  gettype  params  i                                                                   matched   false                      break                                                if  matched                   call user func array array  this  constructor- gt getName                          params                    finish   true                  break                                   unset  constructor            if   finish               throw new  InvalidArgumentException  Cannot match construct by params                         To use it   class MultiConstructorClass       use GenericConstructorOverloadTrait       private  param1       private  param2       private  param3       public function   construct1  param1  array  param2                 this- gt param1    param1           this- gt param2    param2             public function   construct2  param1  array  param2   DateTime  param3                 this- gt   construct1  param1   param2            this- gt param3    param3                         return  DateTime             public function getParam3                 return  this- gt param3                         return array             public function getParam2                 return  this- gt param2                         return mixed             public function getParam1                 return  this- gt param1

User · Answer

You could do something like this   public function   construct  param        if is int  param               this- gt id    param        elseif is object  param             do something else

User · Answer

as stated in the other comments  as php does not support overloading  usually the  type checking tricks  in constructor are avoided and the factory pattern is used intead  ie     myObj   MyClass  factory  fromInteger    params    myObj   MyClass  factory  fromRow    params

User · Answer

You could do something like the following which is really easy and very clean   public function   construct             arguments   func get args         switch sizeof func get args                    case 0    No arguments         break       case 1    One argument          this- gt do something  arguments 0             break                    case 2     Two arguments          this- gt do something else  arguments 0    arguments 1             break

User · Answer

PHP is a dynamic language  so you can t overload methods  You have to check the types of your argument like this   class Student       protected  id     protected  name        etc      public function   construct  idOrRow       if is int  idOrRow                  this- gt id    idOrRow             other members are still uninitialized           else if is array  idOrRow                 this- gt id    idOrRow- gt id          this- gt name    idOrRow- gt name            etc

User · Answer

This question has already been answered with very smart ways to fulfil the requirement but I am wondering why not take a step back and ask the basic question of why do we need a class with two constructors  If my class needs two constructors then probably the way I am designing my classes needs little more consideration to come up with a design that is cleaner and more testable   We are trying to mix up how to instantiate a class with the actual class logic   If a Student object is in a valid state  then does it matter if it was constructed from the row of a DB or data from a web form or a cli request   Now to answer the question that that may arise here that if we don t add the logic of creating an object from db row  then how do we create an object from the db data  we can simply add another class  call it StudentMapper if you are comfortable with data mapper pattern  in some cases you can use StudentRepository  and if nothing fits your needs you can make a StudentFactory to handle all kinds of object construction tasks   Bottomline is to keep persistence layer out of our head when we are working on the domain objects

User · Answer

As of version 5 4  PHP supports traits  This is not exactly what you are looking for  but a simplistic trait based approach would be   trait StudentTrait       protected  id      protected  name       final public function setId  id             this- gt id    id          return  this             final public function getId     return  this- gt id         final public function setName  name             this- gt name    name           return  this             final public function getName     return  this- gt name        class Student1       use StudentTrait       final public function   construct  id     this- gt setId  id        class Student2       use StudentTrait       final public function   construct  id   name     this- gt setId  id - gt setName  name         We end up with two classes  one for each constructor  which is a bit counter-productive  To maintain some sanity  I ll throw in a factory   class StudentFactory       static public function getStudent  id   name   null            return              is null  name                    new Student1  id                    new Student2  id   name            So  it all comes down to this    student1   StudentFactory  getStudent 1    student2   StudentFactory  getStudent 1   yannis      It s a horribly verbose approach  but it can be extremely convenient

[php] Best way to do multiple constructors in PHP

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