Possible Type Constraints

rascal-0.40.17

php-analysis-0.2.4

This is design inspiration for the type inference algorithm.

Declarations:

There are differnt 'levels' of constraints.

On global level (what classes and functions do exist, what variables)
?? not sure: on namespace level...
On class level (what fields and methods are there, what extends/implements)
On function/method level (what variables are used within the scope)
Between scopes (for method calls)

Types:

a variable $a has { t1, ..., tn } types. (within a certain scope)
assignement of variables: $x = $y (types of y = types of x)
return (method|function) can have {} of types: typeof x->a(); is the return value of public function a()
> this means that methods
call constructor when initializing a method
result of expression (e.g. $x + $y) has a set of possible types.
handle magic methods:
- instantiation -> __construct (return type = null);
- method call -> __call

Variable

The type of a variable is the type of the disjunction of all occurances of the variable within a within the scope.
On scopes:
- global scope
- function scope
- method scope
- exception for global key word, it is in the global scope AND in the function/method scope

Constants

Constant

Interface

Decl: name of the interface
Decl: extends (= subtype of ...)

Trait

?? out of scope ?? (not used alot, yet... can be added later)

Class

Decl: name of the class (including namespace)
Decl: extends (= subtype of ...)
Decl: implement
Decl: has constructor
Decl: constructor minimum re quired fields

Class Constant

Decl: name of the constant
Decl: class of the constant
Decl: type of the constant (?)

Class Property

Decl: name of the property
Decl: class of the property

Class Methods (/function)

Decl: name of the method
Decl: has parameter constraints (see below)
Decl: which class the method is in
The return type is the disjunction of the types of all return statements (or void/null when none provided)

Function

Decl: name of the function (including namespace)
Decl: has parameter constraints (see below)
The return type is the disjunction of the types of all return statements (or void/null when none provided)

Actual Parameter constraints

Decl: Minimum required params
Decl: type hints

Cast operators

Casts	Input	Output	Rascal	Notes
(array)	anything	array	`cast(array(), Expr e)`
(bool\|boolean)	anything	boolean	`cast(\bool(), Expr e)`
(int\|integer)	anything	int	`cast(\int(), Expr e)`
(float\|double\|real)	anything	double	`cast(float(), Expr e)`
(string)	anything besides an object\	string	`cast(string(), Expr e)`
(string)	Object	string or fatal error	`cast(string(), Expr e)`	* only works if the object has __toString and returning a string
(object)	anything	object	`cast(object(), Expr e)`
(unset)	anything	NULL	`cast(unset(), Expr e)`

Arithmetic Operators:

please note that the priority is top to bottom (this can be implemented using rascal pattern matching).
'_' matches any type
Division and Modulus can trigger 'division by zero' warnings...

Rules for Negation operator: `-l` -> (double | int)

`l`	result
array	error
double	double
_	integer

Rules for Addition operator: `l + r` -> (array | double | int)

`l`	`r`	result
array	array	array
array	_	fatal error
_	array	fatal error
double	_	double
_	double	double
_	_	integer

Rules for Division operator: `l / r` -> (double | int)

`l`	`r`	result
_	array	fatal error
array	_	fatal error
double	_	double
_	double	double
_	_	integer

Rules for Modulus operator: `l % r` -> (int)

`l`	`r`	result
_	_	integer

Assignment Operators:

Code	typeOf(`$b`)	typeOf(`$a`)	Notes
`$a &= $b;`	_	integer
`$a \\|= $b;`	_	integer
`$a ^= $b;`	_	integer
`$a <<= $b;`	_	integer
`$a >>= $b;`	_	integer
`$a %= $b;`	_	integer
`$a .= $b;`	object*	error	*when object has no __toString() method
`$a .= $b;`	_	string
`$a /= $b;`	array	error
`$a /= $b;`	_	integer
`$a -= $b;`	array	error
`$a -= $b;`	_	integer
`$a *= $b;`	bool\|int\|null	integer
`$a *= $b;`	_	double
`$a += $b;`	bool\|int\|null	integer
`$a += $b;`	_	double

Rules for Bitwise Or (exclusive or) operator: `$a ^ $b`

typeOf(`$a`)	typeOf(`$b`)	Result	Notes
string	string	string
_	_	integer

Rules for Bitwise Shift right operator: `$a >> $b`

typeOf(`$a`)	typeOf(`$b`)	Result	Notes
_	_	integer	always an integer

Rules for Bitwise Not operator: `~$a`

typeOf(`$a`)	Result	Notes
integer\|double	integer
string	string
_	error

Rules for Greater or equal operator: `$a >= $b`

typeOf(`$a`)	typeOf(`$b`)	Result	Notes
_	_	boolean	always a boolean

Rules for Post-increment operator: `$a++`

typeOf(`$a`)	Result	Notes
string	{string\|integer\|double}
null	integer
_	_	other types do not change type

Rules for Post-decrement operator: `$a--`

typeOf(`$a`)	Result	Notes
string	{string\|integer\|double}
_	_	other types do not change type

Rules for Or then operator: `$a || $b`

typeOf(`$a`)	typeOf(`$b`)	Result	Notes
_	_	boolean	always a boolean

assignments

$b = $a // (sub)typeOf($b) is (sub)typeOf($a)
$c = $b = $a; // (sub)typeOf($a) = (sub)typeOf($b) && (sub)typeOf($b) = (sub)typeOf($c) 

class instantiation

$a = new A; // type of $a is class with name "A"; (FQN: Full Qualified Name)
            // minimum required params = 0;
$a = new A(1);  // type of $a is class with name "A"; (FQN: Full Qualified Name)
                // minimum required params = 0 OR 1;

Ternary operator (elvis)

$a ? $b : $c // result of this whole expression is: typeOf($b) OR typeOf($c)

Assumption

I assume that the program is correct. But because it is hard to check if programs are fine in dynamic languagues this is a thread to validity.

Other

?? Adding scope constraints??

hasClassConstant(classDecl, constDecl)
classCont(constDecl, value)
Examples:

    hasClassConstant("A", "C");
        > class A { const C = 1; }
    
    hasField("A", "F");
        > class A { public $F; }

    hasMethod("A", "M");
        > class A { public function M () {} }
    
Subtypes:

    isSubType("A", "B")
        > class A extends B {}  

Note: add default classes, functions, variables and constants to the list of declarations

Symbols:

a <: b          | b is a subtype of a; 
                | example: class b extends a {}

$a = $b;        | subtype of a is the subtype of b
                | syntax: varType($a) <: varType($b);

$a->call()      | typeOf(a) has method "call" OR magic method __call

$a->call($b)    | typeOf(a) has method "call" OR magic method __call
                | typeOf(b) is a subtype of formal parameter 1
                
// minimum number of params 

Constraint Examples

syntax below: 

php code        # constraint that can be derifed


class A {}      # Type A is defined here.

$a = new A{};   # $a is of type A;
$b = $a;        # $b is the same type as $a; ==> eq(typeOf(a),typeOf(b))
$b->do();       # type (or supertype) of $b has method "do"

$c = $b->do(new O)  # type (or supertype) of b has method "do"
                    # return of b->do is of type c
$foo->call()->bar->chain();
    # type of field bar has method "chain"

How to solve constraints: Keep resolving till you have non left.

Advantages: (what can we use it for?)

IDE support!!
Perform better (static) code analysis
Find source code l

Types:​

Variable​

Constants​

Interface​

Trait​

Class​

Class Constant​

Class Property​

Class Methods (/function)​

Function​

Actual Parameter constraints​

Cast operators​

Arithmetic Operators:​

Rules for Negation operator: -l -> (double | int)​

Rules for Addition operator: l + r -> (array | double | int)​

Rules for Division operator: l / r -> (double | int)​

Rules for Modulus operator: l % r -> (int)​

Assignment Operators:​

Rules for Bitwise Or (exclusive or) operator: $a ^ $b​

Rules for Bitwise Shift right operator: $a >> $b​

Rules for Bitwise Not operator: ~$a​

Rules for Greater or equal operator: $a >= $b​

Rules for Post-increment operator: $a++​

Rules for Post-decrement operator: $a--​

Rules for Or then operator: $a || $b​

assignments​

class instantiation​

Ternary operator (elvis)​

Assumption​

Other​

Note: add default classes, functions, variables and constants to the list of declarations​

Constraint Examples​