system/Autoloader/Autoloader.php
public function loadClass(string $class)
	{
		$class = trim($class, '\\');
		$class = str_ireplace('.php', '', $class);

		$mapped_file = $this->loadInNamespace($class);

		// Nothing? One last chance by looking
		// in common CodeIgniter folders.
		if (! $mapped_file)
		{
			$mapped_file = $this->loadLegacy($class);
		}

		return $mapped_file;
	}
public function loadClass(string $class)
	{
		$class = trim($class, '\\');
		$class = str_ireplace('.php', '', $class);

		$mapped_file = $this->loadInNamespace($class);

		// Nothing? One last chance by looking
		// in common CodeIgniter folders.
		if (! $mapped_file)
		{
			$mapped_file = $this->loadLegacy($class);
		}

		return $mapped_file;
	}
Loads the class file for a given class name.

@param string $class The fully qualified class name.

@return string|false The mapped file on success, or boolean false
on failure.