Level 7: has* checks

[hultberg]

Consider the following code:

<?php declare(strict_types = 1);

class HelloWorld
{
	public $obj = null;
	
	public function getObj(): ?HelloWorld
	{
		return $this->obj;
	}
	
	public function hasObj(): bool
	{
		return !is_null($this->obj);
	}
}

$c = new HelloWorld();

if ($c->hasObj()) {
	$c->getObj()->getObj();
}

Here, phpstan will report the following error:

 ------ ------------------------------------------------------------------------- 
  Line   analyzed.php                                                             
 ------ ------------------------------------------------------------------------- 
  21     Calling method getObj() on possibly null value of type HelloWorld|null.  
 ------ ------------------------------------------------------------------------- 

I can understand this error as I have declared getObj to return null or HelloWorld instance, however, this can never occur because of my hasObj check, but phpstan does not seem to understand this. Is this a bug or feature request?

https://phpstan.org/r/2c5f7204f766e044cf3bb54192c84b2e

Cheers

[hultberg]

I was unable to find duplicates while searching, so I reported this just to make sure it is reported. :-)

[JanTvrdik]

@hultberg That's expected behavior. TypeScript would report the same error.

[ondrejmirtes]

Hi, this would require a new type of an extension - "type-specifying extension" to help PHPStan make sure that something is of a specific type after a function or method is called.

But for now, I recommend you the following structure:

• find methods that return nullable type
• has methods (that you already have) that return bool
• get methods that return the type without null (no ? in typehint)

If you ask has before calling get then your code is typesafe. I'm doing this (and know about other projects that do this as well) and it's great.

[ondrejmirtes]

This is already possible on dev-master. The Type-specifying extension support will be released as part of 0.10 during Q2 2018. See some examples on how to write type-specifying extensions:

• "After calling $scope->isInClass(), $scope->getClassReflection() cannot return null": https://github.com/phpstan/phpstan/blob/master/src/Internal/ScopeIsInClassTypeSpecifyingExtension.php
• assert() function support: https://github.com/phpstan/phpstan/blob/master/src/Type/Php/AssertFunctionTypeSpecifyingExtension.php
• is_numeric() function support: https://github.com/phpstan/phpstan/blob/master/src/Type/Php/IsNumericFunctionTypeSpecifyingExtension.php

Let me know if you need any help with writing such an extension.