4. Operators

Operators are used with one or more values (or expressions) which yields another value (so that the operator itself becomes an expression). Expressions can be combinations of operators, functions and variables. Below are the available operator types described. Note that operators are always part of expressions. If no parentheses are used when combining multiple operators within a statement, the expression is resolved from left to right. Therefore, the expression 2 + 2 . "test" will return "4test". The exception is multiplication, division and modulus, which has higher priority than plus and minus.

4.1. Assignment

Assignments will store the value of the expression to the right of the equal sign (=) in a variable to the left. An expression consisting of an assignment will have the value that was assigned. This is useful when assigning a variables in e.g. if statements.

$var = 42;
if (($random = rand(0, 9)) > 5) echo "$random is larger than 5";

4.1.1. Augmented assignment

Augmented assignment operators are documented in the arithmetic chapter.

$var = 5;
$var = $var + 5; // 10

$var = 5;
$var += 5; // 10


Assignments which could be written as augmented assignments are automatically optimized as such by the compiler.


An assignment to “self” (the same variable) on the right side of an augmented assignment yields “undefined” behavior and should not be relied upon.

$var = 5;
$var += ($var = 10);

4.1.2. Destructuring assignment

Destructuring assignment assigns variables with values taken from an array value. If the value is not an array, all variables will be assigned none (rest variables defaults to an empty array) or its default value.

[$a, $b, $c = 3] = [1, 2];
echo $a; // 1
echo $b; // 2
echo $c; // 3 // default value

The rest variable syntax may be used to collect the rest of the array values in a destructuring assignment. This variable has to come last in the destructuring assignment list. The type of the rest variable is always an array.

[$a, $b, ...$c] = [1, 2, 3, 4];
echo $c; // [3, 4]

Keyed index assignments are also supported.

        "result" => $result = [],
        "error" => $error = none,
        "dnssec" => $dnssec = false
] = dns_query("halon.io", ["extended_result" => true]);

It’s however not possible to mix keyed with unkeyed assignments.


If there is less variables in the assignment list than array values, the remaining values will be discarded. If you don’t use the rest variable syntax.

[$a] = [0, 1, 2];
[$a, ...$c] = [1, 2, 3];

If there is more variables in the assignment list than array values, the remaining variables will be assigned the value of none (rest variables defaults to an empty array) or its default value.

[$a, $b = 1, $c = 2] = [0];
[$a, $b, ...$c] = [1, 2];

4.1.3. Slice assignment

Slice assignments uses the slicing syntax to add, remove or replace items in an array by using the slice operator on the left side of an assigment. The slice referred to will be removed while the items on the right side of the assigment operator will be inserted in place right after the removed items.

$var = [1, 2, 7, 5];
$var[2:3] = [3, 4]; // 1, 2, 3, 4, 5

4.2. Arithmetic

These are the arithmetic operators supported, most of which operates on numbers. The operator associativity follow the rules of most languages (e.g. C); explicit parentheses may be added to change or clarify the expression.

$var = (3 - 2) + 2;
  Operator Augmented assignment Augmented assignment expansion
Addition + += x = x + y
Increment ++   x++ and ++x
Subtraction - -= x = x - y
Decrement --   x-- and --x
Multiplication * *= x = x * y
Division / /= x = x / y
Modulus % %= x = x % y
Exponentiation ** **= x = x ** y
Concatenation . .= x = x . y
Precedence Operator Associativity
1 . Left to right
2 + - Left to right
3 * / % Left to right
4 ** Right to left


HSL has constant folding, so numeric calculations are done at compile-time. Which means that 3600 * 24 is just as fast as using the constant 86400.


The ** operator should be used for performance instead of the pow() function.

4.3. String

Strings support the subscript and slicing operator documented in the array section.

4.3.1. Concatenation

It’s possible to use the . concatenation operator on any data type (except None), in which case both operands will be casted to a string.

echo "Hello " . "World";
echo "A number " . 5.5;
echo 1.0 . 2.5; // "12.5"

4.3.2. Format

The string format operator %, allows you to interpolate values into a string using different format specifiers. On the left side of the operator is the template string and on the right side of the operator there must be an array with values.

argument “[” integer “]”
fill “’” <any character>
align “<” (left) | “>” (right) | ”^” (center) | “=” (align after sign)
width integer
precision integer
type “s” (string) | “f” (number) | “x” (hex) | “c” (char) | “b” (binary)

The default argument is the next value in the array. If an argument is specified (indexed at zero), the next implicit argument is n + 1. The default fill character is a space, but that can be changed to any characters. The default alignment is left with the exception for numbers which has right. For strings the precision acts as a cut-off point (max length). Unsupported options for a specific type is simply ignored. To print a literal % in a format string replace it with %%.

echo "Hello %s!" % [ "World" ];

4.3.3. Repeat

Strings may be repeated mutiple times using the * multiplication operator. It doesn’t matter on which side of the operator the multiplier is.

echo "x" * 8; // xxxxxxxx
echo 8 * "x"; // xxxxxxxx

4.4. Array

4.4.1. Subscript

Single items in arrays can be accessed using the subscript ([]) operator. This operator may be used on variables, literals or functions.

If reading and the index doesn’t exist, None is returned.

$var = ["bar", "bar"];
echo $var[2]; // not found none is returned

If assigning to a variable and the index is not found, the variable is converted to an array and the item is created.

$var = [];
$var[2] = "baz";
echo $var[2]; // "baz"

If assigning to a variable and the subscript operator is empty [], the item will be appended to the array (the variable is converted to an empty array first if needed).

$var = [];
$var[] = "baz";
echo $var[0]; // "baz"

Numeric indexes are zero based. If the indexing is sequential (starting from zero) the array allows for direct access (random access) where reads and stores are done in constant O(1) time.

| H | a | l | o | n |
  0   1   2   3   4

It’s possible to chain the index operator with the [:] slicing operator.

The following key casting rules apply.

  • Booleans are casted to numbers (0 and 1).
  • Strings (“1”) containing integers are casted to numbers (1).
  • Numbers (1.10) are casted to integers (1) ignoring the decimal part (x.10). 32bit signed integers are used.
  • All other values are matched as-is.
echo ["1"=>123]; // [1=>123]
echo [1.9=>123]; // [1=>123]
echo ["1.9"=>123]; // ["1.9"=>123]


Use the isset() function to check if a key (index) exists in an array.

4.4.2. Slicing

Slicing is done using the [first:last:step] operator. The indexes of each side of the : may be omitted, first index default to 0, and last index default to the length of the input, thus [:] will return a copy of the inputs values but the keys will re-indexed (numerically). The first index is inclusive and the last index is exclusive. Negative indexes are supported. If indexes causes out-of-bound, an empty type (array or string) is returned. The slicing operator works the same on arrays and strings. Indexes are counted as if the input was iterated; thus associative arrays have no special meaning. The step argument is default 1 thus returning all elements in the sequence, but it can be used to eg. every even (2) item. If the step is negative (eg -1) the sequence will be iterated backwards, causing the elements to be returned in reverse order.

 | H | a | l | o | n |
 0   1   2   3   4   5
-5  -4  -3  -2  -1
$test = "Halon";
echo $test[:]; // Halon
echo $test[1:4]; // alo
echo $test[-1:]; // n
echo $test[-3:]; // lon
echo $test[-5:-2]; // Hal
echo $test[:2] . $test[2:]; // Halon
echo "Halon"[::-1]; // "nolaH"

4.4.3. Push and pop

Operation HSL PHP
shift $array = $array[1:]; array_shift($array);
unshift $array = [“item”] + $array; array_unshift($array, “item”);
pop $array = $array[:-1]; array_pop($array);
push $array = $array + [“item”]; array_push($array, “item”);
push $array = $array + “item”; array_push($array, “item”);
push $array[] = “item”; array_push($array, “item”);

When adding two arrays together, associative keys will be merged (the first array’s data will overwritten where keys conflict) and numeric indexes will be incremented (regardless if they conflict or not).

4.4.4. Removing

In order to remove specific value(s) from an array (and if push and pop is not appropriate) use the subtraction (-) operator to remove based on value (all value matched will be removed) and unset() to remove based on a specific key (index) or slice. The subtraction operator supports both single items and arrays (where all values will be removed). The array will not be re-indexed (for that use the slice operator ($var = $var[:]).

echo ["foo", 5] - 5; // [0=>"foo"]
echo ["foo", "foo", 5] - "foo"; // [2=>5]
echo ["foo", 5] - ["foo", 5]; // []


Use the unset() function to unset values based on the key (index) or slice.

4.4.5. Repeat

Arrays may be repeated mutiple times using the * multiplication operator. It doesn’t matter on which side of the operator the multiplier is.

echo ["x", "y"] * 2; // [x, y, x, y]
echo 8 * ["x", "y"]; // [x, y, x, y]

4.4.6. Spread

The spread operator allows arrays to be expanded in place of multiple arguments in function calls and in array literals.

$parts = ["second", "second to last"];
echo ["first", ...$parts, "last"];
// [0=>"first",1=>"second",2=>"second to last",3=>"last"]

4.5. Logic (boolean)

Logic operators treats all expressions and variables as either true or false. The truthiness depends on the data type.

Test Operator Descriptions
and and And operator
or or Or operator
not not Not operator
not ! Not operator

4.5.1. Short-circuit evaluation

The and and or operations are short-circuit. They will only evaluate the right statement if the left one doesn’t satisfy the condition. In the example below, bar() is not executed because foo() return true, thus satisfying the condition.

function foo() { return true; }
function bar() { return false; }

if (foo() or bar()) echo "foo or bar";

4.6. Bitwise

Bitwise operators treat their operands as 32 bits signed integers (except for zero-fill right shift >>> which is unsigned) in two’s complement format. The result of these operators are regular numbers.

Test Operator Descriptions
and & Bitwise AND operator
or | Bitwise OR operator
xor ^ Bitwise XOR operator
not ~ Bitwise NOT operator
<< << Shift left, padded with zeros
>> >> Shift right, sign-propagating
>>> >>> Shift right, zero-fill
$flags = 5;

$flagA = 0b0001;
$flagB = 0b0010;
$flagC = 0b0100;
$flagD = 0b1000;
if ($flags & ($flagB | $flagC)) echo "match";

4.7. Comparison

These operators compare the expressions (operands) on both sides of the operator with one another, and the expression return either true or false if they matched.

Test   Description Works on types
loose equality == Matches for equality Any
loose inequality != Matches for inequality Any
strictly typed equality === Matches for strict equality Any
strictly typed inequality !== Matches for strict inequality Any
less than < Matches for less than Numbers
greater than > Matches for greater than Numbers
less or equal than <= Matches for less or equal than Numbers
greater or equal than >= Matches for greater or equal than Numbers
regular expression =~ Matches for equality using regular expressions Strings
inequality regular expression !~ Matches for inequality using regular expressions Strings

4.7.1. Loose equality table

If comparing two operands of different data type using the == operator, the result may be “unexpected”, therefore you should preferable always explicitly convert them using functions like number() and string().

A \ B None Boolean Numbers String Vector Function Object Resource
None true false false false false false false false
Boolean false A === B number(A) === B A === boolean(B) A === boolean(B) A === boolean(B) A === boolean(B) A === boolean(B)
Numbers false A === number(B) A === B A === number(B) A == boolean(B) A == boolean(B) A == boolean(B) A == boolean(B)
String false boolean(A) === B number(A) === B A === B false false false false
Vector false boolean(A) === B boolean(A) == B false A === B false false false
Function false boolean(A) === B boolean(A) == B false false A === B false false
Object false boolean(A) === B boolean(A) == B false false false A === B false
Resource false boolean(A) === B boolean(A) == B false false false false A === B

4.7.2. Truthiness

Truthiness of a value tells if the value is considered true eg. when using them as conditions in if statements.

Type Truthiness
None false
Boolean x
Numbers x != 0
String ! empty(x)
Vector ! empty(x)
Function true
Object true
Resource true

4.7.3. Regular expression

The regular expression operator (=~ and not-match !~ operator) matches a string by default using partial matching against a regular expression. That means it allows a substring to match. To explicit mark the beginning or end of a pattern, use ^ for beginning and $ for the end.

if ($var =~ #/\bhalon\b/) echo "contain the word halon";


If using raw strings with regular expressions there is no need to escape some characters twice. Literal strings (both double-quoted (without variable interpolation) and raw strings) as regular expressions will be precompiled for greater performance.

See also

For data extraction using regular expressions see pcre_match() family of functions.

4.8. Function

4.8.1. Call

Functions may be called using the () operator. It applies to both regular functions as well as anonymous functions and named function pointers.

$multiply = function ($x, $y) { return $x * $y };
echo $multiply(3, 5); // 5

4.9. Class

4.9.1. Property

The property operator (->) may be used to access (non-static) variables and functions on objects (class instances). It acts the same as the subscript operator ([]).

class makeCounter
        constructor() { $this->n = 0; }
        function inc() { $this->n += 1; }
        function get() { return $this->n; }
$counter1 = makeCounter();

$counter1->inc();   // 1
$counter1["inc"](); // 2
echo $counter1->get(); // prints 2

4.9.2. Scope resolution

The scope resolution operator (::) is used to access static variables and functions on classes.

class-name :: function
class-name :: $variable
class MyClass
        static $x = 5;
        static function getX() { return MyClass::$x; }
echo MyClass::$x; // 5
echo MyClass::getX(); // 5 Static

The scope resolution operator can use the static keyword in the same class as a shorthand for the class name itself.

class MyClass
        static $x = 5;
        static function getX() { return static::$x; }