yii\helpers\BaseVarDumper::exportClosure PHP Method

    private static function exportClosure(\Closure $closure)
    {
        $reflection = new \ReflectionFunction($closure);
        $fileName = $reflection->getFileName();
        $start = $reflection->getStartLine();
        $end = $reflection->getEndLine();
        if ($fileName === false || $start === false || $end === false) {
            return 'function() {/* Error: unable to determine Closure source */}';
        }
        --$start;
        $source = implode("\n", array_slice(file($fileName), $start, $end - $start));
        $tokens = token_get_all('<?php ' . $source);
        array_shift($tokens);
        $closureTokens = [];
        $pendingParenthesisCount = 0;
        foreach ($tokens as $token) {
            if (isset($token[0]) && $token[0] === T_FUNCTION) {
                $closureTokens[] = $token[1];
                continue;
            }
            if ($closureTokens !== []) {
                $closureTokens[] = isset($token[1]) ? $token[1] : $token;
                if ($token === '}') {
                    $pendingParenthesisCount--;
                    if ($pendingParenthesisCount === 0) {
                        break;
                    }
                } elseif ($token === '{') {
                    $pendingParenthesisCount++;
                }
            }
        }
        return implode('', $closureTokens);
    }