🪡 Template Strings

for Symfony Expression Language (5-8)

What looks like a dot, a cross and a wave, and does the same thing?

It's the string concatenation operator, of course!

PHP uses a dot/period (.), many languages including JavaScript use +, whereas Symfony Expression Language uses the tilde (~).

This library provides a translation layer on top of Expression Language that converts template strings in ES6 format* to a valid expression. While an updated Expression Language subclass wrapper is provided for convenience, you don't have to use it – you can use the provided trait instead.

* only ES6 string interpolation (with any expressions and nesting) is supported; f.e. tagged templates are not.

🔌 Installation

As always, the recommended and easiest way to install this library is through Composer:

composer require "uuf6429/expression-language-tplstring"

🚀 Usage

If you do not plan on extending Symfony Expression Language class, you can use the provided drop-in:

$el = new \uuf6429\ExpressionLanguage\ExpressionLanguageWithTplStr();
$result = $el->evaluate('`hello ${name}!`', ['name' => 'mars']);
assert($result === 'hello mars!');

Otherwise, you can also use the provided trait:

use uuf6429\ExpressionLanguage\TemplateStringTranslatorTrait;
use Symfony\Component\ExpressionLanguage\ExpressionLanguage as SymfonyExpressionLanguage;
use Symfony\Component\ExpressionLanguage\ParsedExpression as SymfonyParsedExpression;

class MyCustomExpressionLanguage
{
    use TemplateStringTranslatorTrait;

    private SymfonyExpressionLanguage $base;

    public function __construct()
    {
        $this->base = new SymfonyExpressionLanguage();
    }

    public function compile($expression, array $names = []): string
    {
        return $this->base->compile($this->processTemplateStrings($expression), $names);
    }

    public function evaluate($expression, array $values = [])
    {
        return $this->base->evaluate($this->processTemplateStrings($expression), $values);
    }
}

$el = new MyCustomExpressionLanguage();
$result = $el->evaluate('`hello ${name}!`', ['name' => 'world']);
assert($result === 'hello world!');

🪆 Nested Template Strings

Since the translator uses a robust state machine, you can nest template strings infinitely:

$el = new \uuf6429\ExpressionLanguage\ExpressionLanguageWithTplStr();
$result = $el->evaluate(
    '`Hello ${user.isMember ? `VIP ${user.name}` : \'Guest\'}!`',
    [
        'user' => (object)[
            'isMember' => true,
            'name' => 'John',
        ],
    ]
);
assert($result === 'Hello VIP John!');

🚨 Robust Error Handling

Unmatched template boundaries (like unclosed backticks , or unclosed ${, or unclosed quotes '/") will immediately trigger a Symfony\Component\ExpressionLanguage\SyntaxError with precise details and position:

$el = new \uuf6429\ExpressionLanguage\ExpressionLanguageWithTplStr();
try {
    $el->evaluate('`hello ${name');
} catch (\Symfony\Component\ExpressionLanguage\SyntaxError $e) {
    assert($e->getMessage() === 'Expected "}" around position 13 for expression ``hello ${name`.');
}