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PHP Type Constraint Operations


Here we document some examples of the type inference constraints we extract from PHP code.

Assign operators (some sort of case)

$a .= ... // $a is a String
$a *= ... // $a is an Integer

$x = (int) $y; // $x = Integer
$x = 1; // $x = Integer

Method call

$a -> methodCall();
// the type of $a has methodCall(); || type of $a has __clone() (magic method)

Conditional statements

$a instanceOf "C" // is_a
// type of $a is (a child of) class C || type of $a implements interface C

is_numeric($a) // $a is numeric
is_bool($a) // $a is a boolean

Member addition

class Empty {}
$e = new Empty();
$e->newField = "value"; // newField is added
echo $e->newField; // newField is used

Return types of methods and functions

function f () { return true }; // return type of f is a boolean

Object instantiation

$x = new Obj; // $x = instance of class Obj

Parameters (number of required params and type hints)

function getPersonId(Person $p) {
return rand(100);
getPersonId(new Person()); // correct
getPersonId(new Person(), 1, 2, true); // correct
getPersonId(); // incorrect

self/static/parent **

self::methodCall(); // current class
parent::methodCall(); // one of the parent classes
static::methodCall(); // class of instantiation

Out of scope

- Variable variables (resolve to everything)
- Variable method calls (resolve to everything)
- Eval

Other Notes

non parsing scripts are ignored