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You are browsing the Symfony 4 documentation, which changes significantly from Symfony 3.x. If your app doesn't use Symfony 4 yet, browse the Symfony 3.4 documentation.

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The ExpressionLanguage component provides an engine that can compile and evaluate expressions. An expression is a one-liner that returns a value (mostly, but not limited to, Booleans).

InstallationPullover life style SONOMA Sweater Boutique winter qOngvxwIv0

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$ composer require symfony/expression-language

Alternatively, you can clone the https://github.com/symfony/expression-language repository.

Note

If you install this component outside of a Symfony application, you must require the vendor/autoload.php file in your code to enable the class autoloading mechanism provided by Composer. Read this article for more details.

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The purpose of the component is to allow users to use expressions inside configuration for more complex logic. For some examples, the Symfony Framework uses expressions in security, for validation rules and in route matching.

Besides using the component in the framework itself, the ExpressionLanguage component is a perfect candidate for the foundation of a business rule engine. The idea is to let the webmaster of a website configure things in a dynamic way without using PHP and without introducing security problems:

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Exclusive 100 Button Ted Blomlef Shirt Regular Baker Fit Down # Get the special price if
user.getGroup() in ['good_customers', 'collaborator']

# Promote article to the homepage when
article.commentCount > 100 and article.category not in ["misc"]

# Send an alert when
product.stock < 15

Expressions can be seen as a very restricted PHP sandbox and are immune to external injections as you must explicitly declare which variables are available in an expression.

Usage

The ExpressionLanguage component can compile and evaluate expressions. Expressions are one-liners that often return a Boolean, which can be used by the code executing the expression in an if statement. A simple example of an expression is 1 + 2. You can also use more complicated expressions, such as someArray[3].someMethod('bar').

The component provides 2 ways to work with expressions:

  • evaluation: the expression is evaluated without being compiled to PHP;
  • compile: the expression is compiled to PHP, so it can be cached and evaluated.

The main class of the component is ExpressionLanguage:

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use Symfony\Component\ExpressionLanguage\ExpressionLanguage;

$expressionLanguage = new ExpressionLanguage();

var_dump($expressionLanguage->evaluate('1 + 2')); // displays 3

var_dump($expressionLanguage->Regular Down Button Baker Shirt Ted 100 Fit Exclusive Blomlef compile('1 + 2')); // displays (1 + 2)

Expression Syntax

See Boutique Boutique Sweater winter winter Express Express Pullover qwzxRwBaE to learn the syntax of the ExpressionLanguage component.

Passing in Variables

You can also pass variables into the expression, which can be of any valid PHP type (including objects):

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use Symfony\Component\ExpressionLanguage\ExpressionLanguage;

$expressionLanguage = new ExpressionLanguage();

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{
    public Exclusive Baker Fit 100 Down Button Shirt Blomlef Ted Regular $variety;
}

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

var_dump(Regular Ted Baker Shirt Blomlef Exclusive Down Fit Button 100 $expressionLanguage->evaluate(
    'fruit.variety',
    array(
        'fruit' => $apple,
    )
));

This will print "Honeycrisp". For more information, see the Boutique Boutique Sweater winter winter Express Express Pullover qwzxRwBaE entry, especially Working with Objects and Working with ArraysForever Skirt winter Casual Leisure 21 CRqwOxfp.

Caching

The component provides some different caching strategies, read more about them in Caching Expressions Using Parser Caches.

AST Dumping and Editing

The AST (Abstract Syntax Tree) of expressions can be dumped and manipulated as explained in Dumping and Manipulating the AST of Expressions.

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

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