woocommerce-paypal-payments/lib/common/Pattern/SingletonDecorator.php

<?php
/**
 * The Singleton Trait can be used to wrap an execution block, so it behaves like a Singleton.
 * It executes the callable once, on subsequent calls returns the same result.
 */

namespace WooCommerce\PayPalCommerce\Common\Pattern;

/**
 * Class SingletonDecorator.
 */
class SingletonDecorator {

	/**
	 * The callable with the executing code
	 *
	 * @var callable
	 */
	private $callable;

	/**
	 * The execution result
	 *
	 * @var mixed
	 */
	private $result;

	/**
	 * Indicates if the callable is resolved
	 *
	 * @var bool
	 */
	private $executed = false;

	/**
	 * SingletonDecorator constructor.
	 *
	 * @param callable $callable
	 */
	public function __construct( callable $callable ) {
		$this->callable = $callable;
	}

	/**
	 * The make constructor.
	 *
	 * @param callable $callable
	 * @return self
	 */
	public static function make( callable $callable ): self {
		return new static( $callable );
	}

	/**
	 * Invokes a callable once and returns the same result on subsequent invokes.
	 *
	 * @param mixed ...$args Arguments to be passed to the callable.
	 * @return mixed
	 */
	public function __invoke( ...$args ) {
		if ( ! $this->executed ) {
			$this->result   = call_user_func_array( $this->callable, $args );
			$this->executed = true;
		}

		return $this->result;
	}
}