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fabpotfabpot
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feature #34013 [DI] add LazyString for lazy computation of string values injected into services (nicolas-grekas)
This PR was merged into the 4.4 branch. Discussion ---------- [DI] add `LazyString` for lazy computation of string values injected into services | Q | A | ------------- | --- | Branch? | 4.4 | Bug fix? | no | New feature? | yes | Deprecations? | no | Tickets | - | License | MIT | Doc PR | - This is an idea I should have had years ago :) By wrapping any callable into a `LazyString`, we allow resolving the corresponding string value lazily (eg because the value comes from a remote server). The tricky parts are memoization and error handling, which are both dealt with in the class. This is currently part of #33997 Commits ------- ccb0365 [DI] add `LazyString` for lazy computation of string values injected into services
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‎src/Symfony/Component/DependencyInjection/CHANGELOG.md

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* made singly-implemented interfaces detection be scoped by file
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* added ability to define a static priority method for tagged service
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* added support for improved syntax to define method calls in Yaml
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* added `LazyString` for lazy computation of string values injected into services
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4.3.0
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-----

‎src/Symfony/Component/DependencyInjection/LazyString.php

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<?php
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/*
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* This file is part of the Symfony package.
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*
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* (c) Fabien Potencier <[email protected]>
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*
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* For the full copyright and license information, please view the LICENSE
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* file that was distributed with this source code.
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*/
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namespace Symfony\Component\DependencyInjection;
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/**
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* A string whose value is computed lazily by a callback.
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*
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* @author Nicolas Grekas <[email protected]>
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*/
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class LazyString
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{
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private $value;
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/**
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* @param callable $callback A callable or a [Closure, method] lazy-callable
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*
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* @return static
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*/
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public static function fromCallable($callback, ...$arguments): self
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{
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if (!\is_callable($callback) && !(\is_array($callback) && isset($callback[0]) && $callback[0] instanceof \Closure && 2 >= \count($callback))) {
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throw new \TypeError(sprintf('Argument 1 passed to %s() must be a callable or a [Closure, method] lazy-callable, %s given.', __METHOD__, \gettype($callback)));
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}
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$lazyString = new static();
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$lazyString->value = static function () use (&$callback, &$arguments, &$value): string {
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if (null !== $arguments) {
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if (!\is_callable($callback)) {
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$callback[0] = $callback[0]();
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$callback[1] = $callback[1] ?? '__invoke';
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}
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$value = $callback(...$arguments);
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$callback = self::getPrettyName($callback);
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$arguments = null;
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}
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return $value ?? '';
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};
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return $lazyString;
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}
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public function __toString()
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{
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if (\is_string($this->value)) {
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return $this->value;
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}
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try {
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return $this->value = ($this->value)();
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} catch (\Throwable $e) {
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if (\TypeError::class === \get_class($e) && __FILE__ === $e->getFile()) {
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$type = explode(', ', $e->getMessage());
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$type = substr(array_pop($type), 0, -\strlen(' returned'));
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$r = new \ReflectionFunction($this->value);
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$callback = $r->getStaticVariables()['callback'];
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$e = new \TypeError(sprintf('Return value of %s() passed to %s::fromCallable() must be of the type string, %s returned.', $callback, static::class, $type));
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}
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if (\PHP_VERSION_ID < 70400) {
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// leverage the ErrorHandler component with graceful fallback when it's not available
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return trigger_error($e, E_USER_ERROR);
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}
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throw $e;
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}
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}
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private function __construct()
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{
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}
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private static function getPrettyName(callable $callback): string
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{
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if (\is_string($callback)) {
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return $callback;
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}
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if (\is_array($callback)) {
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$class = \is_object($callback[0]) ? \get_class($callback[0]) : $callback[0];
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$method = $callback[1];
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} elseif ($callback instanceof \Closure) {
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$r = new \ReflectionFunction($callback);
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if (false !== strpos($r->name, '{closure}') || !$class = $r->getClosureScopeClass()) {
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return $r->name;
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}
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$class = $class->name;
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$method = $r->name;
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} else {
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$class = \get_class($callback);
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$method = '__invoke';
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}
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if (isset($class[15]) && "\0" === $class[15] && 0 === strpos($class, "class@anonymous\x00")) {
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$class = get_parent_class($class).'@anonymous';
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}
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return $class.'::'.$method;
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}
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}

‎src/Symfony/Component/DependencyInjection/Tests/LazyStringTest.php

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<?php
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/*
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* This file is part of the Symfony package.
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*
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* (c) Fabien Potencier <[email protected]>
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*
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* For the full copyright and license information, please view the LICENSE
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* file that was distributed with this source code.
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*/
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namespace Symfony\Component\DependencyInjection\Tests;
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use PHPUnit\Framework\TestCase;
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use Symfony\Component\DependencyInjection\LazyString;
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use Symfony\Component\ErrorHandler\ErrorHandler;
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class LazyStringTest extends TestCase
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{
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public function testLazyString()
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{
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$count = 0;
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$s = LazyString::fromCallable(function () use (&$count) {
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return ++$count;
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});
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$this->assertSame(0, $count);
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$this->assertSame('1', (string) $s);
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$this->assertSame(1, $count);
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}
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public function testLazyCallable()
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{
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$count = 0;
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$s = LazyString::fromCallable([function () use (&$count) {
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return new class($count) {
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private $count;
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public function __construct(int &$count)
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{
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$this->count = &$count;
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}
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public function __invoke()
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{
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return ++$this->count;
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}
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};
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}]);
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$this->assertSame(0, $count);
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$this->assertSame('1', (string) $s);
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$this->assertSame(1, $count);
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$this->assertSame('1', (string) $s); // ensure the value is memoized
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$this->assertSame(1, $count);
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}
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/**
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* @runInSeparateProcess
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*/
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public function testReturnTypeError()
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{
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ErrorHandler::register();
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$s = LazyString::fromCallable(function () { return []; });
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$this->expectException(\TypeError::class);
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$this->expectExceptionMessage('Return value of '.__NAMESPACE__.'\{closure}() passed to '.LazyString::class.'::fromCallable() must be of the type string, array returned.');
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(string) $s;
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}
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}

‎src/Symfony/Component/DependencyInjection/composer.json

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"require-dev": {
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"symfony/yaml": "^3.4|^4.0|^5.0",
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"symfony/config": "^4.3|^5.0",
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"symfony/error-handler": "^4.4|^5.0",
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"symfony/expression-language": "^3.4|^4.0|^5.0"
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},
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"suggest": {

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