6 responses to “Do while false in PHP?”

1. 

   Pablo

   May 20, 2018 at 9:29 am

   You’re wrong. GOTO allows you to go everywhere in the code. The statement do not!
   DO{…}WHILE(FALSE); simply let you exit the loop, exactly like a return in a function does.

   Have you ever had a lot of IF-ELSE nested used only to test the requirements?

   For example:
   $person = array();
   $person[‘lastname’] = sanitize($_POST[‘lastname’]);
   if($person[‘lastname’]==””)
   {
   $error = “Empty last name”;
   } else {
   if(strlen($person[‘lastname’])>30)
   {
   $error = “Last name is too long”;
   } else {
   $person[‘firstname’] = sanitize($_POST[‘firstname’];
   if($person[‘firstname’]==””)
   {
   $error = “First name is empty”;
   } else {
   //…do a lot of other suff
   }//end if firstname is empty
   }//end if lastname length
   }//end if firstname is empty

   It can be useful write a function like:
   function checkPerson()
   {
   $person = array();
   $person[‘lastname’] = sanitize($_POST[‘lastname’]);
   if($person[‘lastname’]==””) {
   return “Empty last name”;
   }//end if lastname is empty
   if(strlen($person[‘lastname’])>30) {
   return “Last name is too long”;
   }//end if lastname length
   $person[‘firstname’] = sanitize($_POST[‘firstname’];
   if($person[‘firstname’]==””) {
   return “First name is empty”;
   }//end if firstname is empty
   //…do a lot of other suff
   }
   Well… the function checks but also gathers and sanitizes the data. How do you get the valid data?

   Now look at this:
   $person = array();
   $error = “”;
   do {
   $person[‘lastname’] = sanitize($_POST[‘lastname’]);
   if($person[‘lastname’]==””)
   {
   $error = “Empty last name”;
   break;
   }//end if lastname is empty
   if(strlen($person[‘lastname’])>30)
   {
   $error = “Last name is too long”;
   break;
   }//end if lastname length
   $person[‘firstname’] = sanitize($_POST[‘firstname’];
   if($person[‘firstname’]==””)
   {
   $error = “First name is empty”;
   break;
   }//end if firstname is empty
   //…do a lot of other suff

   } while(false);

   Which list of IF-ELSEs is more readble? Which list of IF-ELSEs is easier to edit?
   Don’t you like DO-WHILE(ELSE) because you can read it? Just remember that in a DO-WHILE statement the code runs first and then condition is checked!
   Well, I suggest you other two ways to write it:
   FOR(;;;)){
   //do stuff
   BREAK;
   }
   SWITCH(TRUE)
   {
   DEFAULT:
   //do stuff
   BREAK;
   }

   Reply
   1. 

      Eric Binnion

      June 13, 2018 at 3:05 pm

      You’re wrong.

      Sure. That happens often. Though, I’m not 100% sure what your point is here.

      In your comment, it seems that you’re arguing that a do while false can be more readable than several if statements. I’m not sure I ever said that it couldn’t. What I did say is that it confused me at first. In my summary, I went on to say that, at a minimum, it probably makes sense to comment a do while false loop so that other developers could get up to speed quickly.

      Reply
      1. 

         Robin J

         October 28, 2019 at 9:32 pm

         I think in almost all cases, especially the one Pablo used in their example, the do-while (false) pattern can and should be refactored into a separate function. If code can be written in such a way that it doesn’t require unexpected usages of programming constructs, and therefore comments to explain said unexpected usages, then it probably should.

         Reply
2. 

   Mr Alexander

   December 9, 2019 at 9:40 am

   I am personally not a fan of this type of statement, instead I prefer to encapsulate the code either within another function, use goto: (if break is used);

   I think it is a little sloppy to use the do while false statement.

   Reply
3. Mending a PHP do…while(false) – C Jane Codex

   January 9, 2021 at 2:09 pm

   […] language attribute to solve a problem. The issue in using a hack is that it makes it difficult for other programmers to understand your code. Additionally using language features in a ways they […]

   Reply
4. 

   Oli

   December 7, 2022 at 3:30 pm

   while(false) can only be used for this purpose. if confused, google it and arrive here

   Reply

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