src/Composer/Cache.php
public function copyTo($file, $target)
    {
        if ($this->enabled) {
            $file = preg_replace('{[^'.$this->whitelist.']}i', '-', $file);
            if (file_exists($this->root . $file)) {
                try {
                    touch($this->root . $file, filemtime($this->root . $file), time());
                } catch (\ErrorException $e) {
                    // fallback in case the above failed due to incorrect ownership
                    // see https://github.com/composer/composer/issues/4070
                    Silencer::call('touch', $this->root . $file);
                }

                $this->io->writeError('Reading '.$this->root . $file.' from cache', true, IOInterface::DEBUG);

                return copy($this->root . $file, $target);
            }
        }

        return false;
    }
public function copyTo($file, $target)
    {
        if ($this->enabled) {
            $file = preg_replace('{[^'.$this->whitelist.']}i', '-', $file);
            if (file_exists($this->root . $file)) {
                try {
                    touch($this->root . $file, filemtime($this->root . $file), time());
                } catch (\ErrorException $e) {
                    // fallback in case the above failed due to incorrect ownership
                    // see https://github.com/composer/composer/issues/4070
                    Silencer::call('touch', $this->root . $file);
                }

                $this->io->writeError('Reading '.$this->root . $file.' from cache', true, IOInterface::DEBUG);

                return copy($this->root . $file, $target);
            }
        }

        return false;
    }
Copy a file out of the cache