how to make if decision in swiftmailer to check if field is empty then do not send `td` to mail

问题

I'm trying to send email(s) after submitting a form, I want to achieve:

1) If field is empty then no need to send table row to mail. Just like the field age below is optional, user might add his/her age or might not, so how to do it in switmail $message->addPart('Message','text/html') function.

I tried but failed saying: Parse error: syntax error, unexpected 'if' (T_IF) in... The issue is only with if.. without if statement everything works fine.

$content = '<table>
   ...
   <tr><td>' . $_POST["firstname"] . '<td></tr>
   ' . if(!empty($_POST["age"])) {
          . '<tr><td>' . $_POST["age"] . '</td></tr>' .
       }
     ...
<table>';
$message->addPart($content, 'text/html');

回答1:

Do it outside of the $content variable.

$age = (!empty($_POST["age"])) ? '<tr><td>' . $_POST["age"] . '</td></tr>' : '';

$content = '<table>
   ...
   <tr><td>' . $_POST["firstname"] . '<td></tr>'
   . $age . '
     ...
<table>';

来源：https://stackoverflow.com/questions/37574112/how-to-make-if-decision-in-swiftmailer-to-check-if-field-is-empty-then-do-not-se