Best practices for static constructors

Question

I want to create an instance of a class and call a method on that instance, in a single line of code.

PHP won't allow calling a method on a regular constructor:

new Foo()->set_sth(); // Outputs an error. 

So I'm using, if I can call it that, a static constructor:

Foo::construct()->set_sth(); 

Here's my question:

Is using static constructors like that considered a good practice and if yes, how would you recommend naming the methods for these static constructors?

I've been hesitating over the following options:

Foo::construct(); Foo::create(); Foo::factory() Foo::Foo(); constructor::Foo(); 

Answer 1

Static constructors (or "named constructors") are only beneficial to prove an intention, as @koen says.

Since 5.4 though, someting called "dereferencing" appeared, which permits you to inline class instantiation directly with a method call.

(new MyClass($arg1))->doSomething(); // works with newer versions of php 

So, static constructors are only useful if you have multiple ways to instantiate your objects. If you have only one (always the same type of arguments and number of args), there is no need for static constructors.

But if you have multiple ways of instantiations, then static constructors are very useful, as it avoids to pollute your main constructor with useless argument checking, weakening languages constraints.

Example:

<?php  class Duration { private $start; private $end;  // or public depending if you still want to allow direct instantiation private function __construct($startTimeStamp = null, $endTimestamp = null) {    $this->start = $startTimestamp;    $this->end   = $endTimestamp; }  public static function fromDateTime(\DateTime $start, \DateTime $end) {     return new self($start->format('U'), $end->format('U')); }  public static function oneDayStartingToday() {     $day = new self;     $day->start = time();     $day->end = (new \DateTimeImmutable)->modify('+1 day')->format('U');      return $day; }  } 

As you can see in oneDayStartingToday, the static method can access private fields of the instance! Crazy isn't it ? :)

For a better explanation, see http://verraes.net/2014/06/named-constructors-in-php/

Answer 2

The naming of any method should be with intention revealing names. I can't tell what 'Foo::factory' does. Try to build to a higher level language:

User::with100StartingPoints(); 

This would be the same as:

$user = new User(); $user->setPointsTo(100); 

You could also easily test whether User::with100StartingPoints() is equal to this.