PHP empty constructor | 易学教程

问题

Just wondering is it best to define an empty constructor or leave the constructor definition out completely in PHP? I have a habit of defining constructors with just return true;, even if I don't need the constructor to do anything - just for completion reasons.

回答1:

If you don't need a constructor it's best to leave it out, no need to write more code. When you DO write it, leave it empty... returning true doesn't have a purpose.

回答2:

There is a difference between the two: If you write an empty __construct() function, you overwrite any inherited __construct() from a parent class.

So if you don't need it and you do not want to overwrite the parent constructor explicitly, don't write it at all.

回答3:

EDIT:

previous answer is no longer valid, since PHP now behaves like other oop programming languages. constructors aren't part of interfaces. therefore you are now allowed to override them how you prefer without any issues whatsoever

the only exception to this is:

interface iTest
{
    function __construct(A $a, B $b, Array $c);
}

class Test implements iTest
{
    function __construct(A $a, B $b, Array $c){}
    // in this case the constructor must be compatible with the one specified in the interface
    // this is something that php allows but that should never be used
    // in fact as i stated earlier, constructors must not be part of interfaces
}

PREVIOUS OLD NOT-VALID-ANYMORE ANSWER:

there is an important difference between an empty constructor and no constructor at all

class A{}

class B extends A{
     function __construct(ArrayObject $a, DOMDocument $b){}
}

VS

class A{
     function __construct(){}
}
class B extends A{
    function __construct(ArrayObject $a, DOMDocument $b){}
}

// error B::__construct should be compatible with A constructor

回答4:

You should only define an empty constructor if your object should never be instantiated. If that is the case, make the __construct() private.

回答5:

constructor always return instance of class in which its defined . Hence you never use "return" inside constructor . Lastly its better not to define it if you are not gona use it .

来源：https://stackoverflow.com/questions/7673160/php-empty-constructor

标签

php

constructor