The Expression Syntax

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The ExpressionLanguage component uses a specific syntax which is based on the expression syntax of Twig. In this document, you can find all supported syntaxes.

Supported Literals

The component supports:

  • strings - single and double quotes (e.g. 'hello')
  • numbers - integers (e.g. 103), decimals (e.g. 9.95), decimals without leading zeros (e.g. .99, equivalent to 0.99); all numbers support optional underscores as separators to improve readability (e.g. 1_000_000, 3.14159_26535)
  • arrays - using JSON-like notation (e.g. [1, 2])
  • hashes - using JSON-like notation (e.g. { foo: 'bar' })
  • booleans - true and false
  • null - null
  • exponential - also known as scientific (e.g. 1.99E+3 or 1e-2)

Caution

A backslash (\) must be escaped by 3 backslashes (\\\\) in a string and 7 backslashes (\\\\\\\\) in a regex:

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echo $expressionLanguage->evaluate('"\\\\"'); // prints \
$expressionLanguage->evaluate('"a\\\\b" matches "/^a\\\\\\\\b$/"'); // returns true

Control characters (e.g. \n) in expressions are replaced with whitespace. To avoid this, escape the sequence with a single backslash (e.g. \\n).

Working with Objects

When passing objects into an expression, you can use different syntaxes to access properties and call methods on the object.

Accessing Public Properties

Public properties on objects can be accessed by using the . syntax, similar to JavaScript:

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class Apple
{
    public string $variety;
}

$apple = new Apple();
$apple->variety = 'Honeycrisp';

var_dump($expressionLanguage->evaluate(
    'fruit.variety',
    [
        'fruit' => $apple,
    ]
));

This will print out Honeycrisp.

Calling Methods

The . syntax can also be used to call methods on an object, similar to JavaScript:

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class Robot
{
    public function sayHi(int $times): string
    {
        $greetings = [];
        for ($i = 0; $i < $times; $i++) {
            $greetings[] = 'Hi';
        }

        return implode(' ', $greetings).'!';
    }
}

$robot = new Robot();

var_dump($expressionLanguage->evaluate(
    'robot.sayHi(3)',
    [
        'robot' => $robot,
    ]
));

This will print out Hi Hi Hi!.

Null-safe Operator

Use the ?. syntax to access properties and methods of objects that can be null (this is equivalent to the $object?->propertyOrMethod PHP null-safe operator):

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// these will throw an exception when `fruit` is `null`
$expressionLanguage->evaluate('fruit.color', ['fruit' => '...'])
$expressionLanguage->evaluate('fruit.getStock()', ['fruit' => '...'])

// these will return `null` if `fruit` is `null`
$expressionLanguage->evaluate('fruit?.color', ['fruit' => '...'])
$expressionLanguage->evaluate('fruit?.getStock()', ['fruit' => '...'])

Null-Coalescing Operator

It returns the left-hand side if it exists and it's not null; otherwise it returns the right-hand side. Expressions can chain multiple coalescing operators:

  • foo ?? 'no'
  • foo.baz ?? 'no'
  • foo[3] ?? 'no'
  • foo.baz ?? foo['baz'] ?? 'no'

Note

The main difference with the null-coalescing operator in PHP is that ExpressionLanguage will throw an exception when trying to access a non-existent variable.

Working with Functions

You can also use registered functions in the expression by using the same syntax as PHP and JavaScript. The ExpressionLanguage component comes with the following functions by default:

  • constant()
  • enum()

constant() function

This function will return the value of a PHP constant:

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define('DB_USER', 'root');

var_dump($expressionLanguage->evaluate(
    'constant("DB_USER")'
));

This will print out root.

This also works with class constants:

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namespace App\SomeNamespace;

class Foo
{
    public const API_ENDPOINT = '/api';
}

var_dump($expressionLanguage->evaluate(
    'constant("App\\\SomeNamespace\\\Foo::API_ENDPOINT")'
));

This will print out /api.

enum() function

This function will return the case of an enumeration:

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namespace App\SomeNamespace;

enum Foo
{
    case Bar;
}

var_dump(App\Enum\Foo::Bar === $expressionLanguage->evaluate(
    'enum("App\\\SomeNamespace\\\Foo::Bar")'
));

This will print out true.

Tip

To read how to register your own functions to use in an expression, see "The ExpressionLanguage Component".

Working with Arrays

If you pass an array into an expression, use the [] syntax to access array keys, similar to JavaScript:

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$data = ['life' => 10, 'universe' => 10, 'everything' => 22];

var_dump($expressionLanguage->evaluate(
    'data["life"] + data["universe"] + data["everything"]',
    [
        'data' => $data,
    ]
));

This will print out 42.

Supported Operators

The component comes with a lot of operators:

Arithmetic Operators

  • + (addition)
  • - (subtraction)
  • * (multiplication)
  • / (division)
  • % (modulus)
  • ** (pow)

For example:

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var_dump($expressionLanguage->evaluate(
    'life + universe + everything',
    [
        'life' => 10,
        'universe' => 10,
        'everything' => 22,
    ]
));

This will print out 42.

Bitwise Operators

  • & (and)
  • | (or)
  • ^ (xor)

Comparison Operators

  • == (equal)
  • === (identical)
  • != (not equal)
  • !== (not identical)
  • < (less than)
  • > (greater than)
  • <= (less than or equal to)
  • >= (greater than or equal to)
  • matches (regex match)
  • contains
  • starts with
  • ends with

Tip

To test if a string does not match a regex, use the logical not operator in combination with the matches operator:

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$expressionLanguage->evaluate('not ("foo" matches "/bar/")'); // returns true

You must use parentheses because the unary operator not has precedence over the binary operator matches.

Examples:

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$ret1 = $expressionLanguage->evaluate(
    'life == everything',
    [
        'life' => 10,
        'everything' => 22,
    ]
);

$ret2 = $expressionLanguage->evaluate(
    'life > everything',
    [
        'life' => 10,
        'everything' => 22,
    ]
);

Both variables would be set to false.

Logical Operators

  • not or !
  • and or &&
  • or or ||

For example:

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$ret = $expressionLanguage->evaluate(
    'life < universe or life < everything',
    [
        'life' => 10,
        'universe' => 10,
        'everything' => 22,
    ]
);

This $ret variable will be set to true.

String Operators

  • ~ (concatenation)

For example:

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var_dump($expressionLanguage->evaluate(
    'firstName~" "~lastName',
    [
        'firstName' => 'Arthur',
        'lastName' => 'Dent',
    ]
));

This would print out Arthur Dent.

Array Operators

  • in (contain)
  • not in (does not contain)

These operators are using strict comparison. For example:

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class User
{
    public string $group;
}

$user = new User();
$user->group = 'human_resources';

$inGroup = $expressionLanguage->evaluate(
    'user.group in ["human_resources", "marketing"]',
    [
        'user' => $user,
    ]
);

The $inGroup would evaluate to true.

Note

The in and not in operators are using strict comparison.

Numeric Operators

  • .. (range)

For example:

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class User
{
    public int $age;
}

$user = new User();
$user->age = 34;

$expressionLanguage->evaluate(
    'user.age in 18..45',
    [
        'user' => $user,
    ]
);

This will evaluate to true, because user.age is in the range from 18 to 45.

Ternary Operators

  • foo ? 'yes' : 'no'
  • foo ?: 'no' (equal to foo ? foo : 'no')
  • foo ? 'yes' (equal to foo ? 'yes' : '')

Other Operators

Operators Precedence

Operator precedence determines the order in which operations are processed in an expression. For example, the result of the expression 1 + 2 * 4 is 9 and not 12 because the multiplication operator (*) takes precedence over the addition operator (+).

To avoid ambiguities (or to alter the default order of operations) add parentheses in your expressions (e.g. (1 + 2) * 4 or 1 + (2 * 4).

The following table summarizes the operators and their associativity from the highest to the lowest precedence:

Operators Associativity
- , + (unary operators that add the number sign) none
** right
*, /, % left
not, ! none
~ left
+, - left
.. left
==, ===, !=, !==, <, >, >=, <=, not in, in, contains, starts with, ends with, matches left
& left
^ left
| left
and, && left
or, || left

Built-in Objects and Variables

When using this component inside a Symfony application, certain objects and variables are automatically injected by Symfony so you can use them in your expressions (e.g. the request, the current user, etc.):

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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