Return a loop in function php

Question

Is it possible to return a loop? not the result but the loop it self. I want to create a function in php. For example like this.

function myloop($sql){
$query = mysql_query($sql);

return while(mysql_fetch_assoc($query))
}

The reason i want to create this is for me to avoid repeating code. Anyone can help me? Thank you..

Why the downvotes? Ok, the question was not the highest quality, but has a good intent - reducing code duplication. Just the idea was not good, but I think this question can arise in many more people too, and providing a good answer to it can be heplful in the future. — ppeterka, Oct 19 '12 at 06:55

score 5 · Answer 1 · edited May 23 '17 at 12:04

5

No, but you can simulate that with an Iterator for stable released PHP as of today. In PHP 5.5 there will be generators that is close, too.

$lazyQuery = new SqlResultItertor($sql);
foreach ($lazyQuery as $assoc) {
    $assoc; # the result, one per row
}

BTW: PDO and MySqli offer this already out of the box (not lazy query, but the result is traversable), for mysql you need to write such an iterator-result object your own.

For some mysql_* functions related code, see this answer. However the general suggestion as of today is to use PDO or mysqli instead, those offer more out of the box. See How to successfully rewrite old mysql-php code with deprecated mysql_* functions?

edited May 23 '17 at 12:04

Community

1
1

answered Oct 19 '12 at 06:51

hakre

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I will try this. I am much more familiar with mysql. But thanks for the tip – thenewbie Oct 19 '12 at 07:13
@thenewbie: You might find this helpful then: http://www.php.net/manual/en/mysqli.quickstart.dual-interface.php - however about the benefits you ask with your question, you want to have an object oriented interface. Mysqli and PDO will help you to not write that much code for that (in the end). – hakre Oct 19 '12 at 07:14

GolezTrol · Accepted Answer · 2012-10-19T07:10:44.497

3

No, you can't. You can pass a function to a function, though:

// The myloop function, with another name.
function query($sql, $rowcallback)
{
  $query = mysqli_query($sql); // use mysqli, not mysql
  while 
    ( ($row = mysql_fetch_assoc($query)) &&
      call_user_func($rowcallback, $row) );
}

// The code to process a row.
function processRow(array $row)
{
   // Use your row here..
   var_dump($row);

   return true; // You can return false to break processing.
}

//calling:
query($yourSelf, 'processRow');

Instead of passing the function by name, you can also use anonymous functions, depending on your php version:

//calling:
query($yourSelf, 
  function(array $row)
  { 
    var_dump($row); 
    return true; // You can return false to break processing.
  });

The function which is called from the callee is often called a callback. call_user_func is the best way to call a callback, since it will also accept methods and static methods, not just functions, so you're more flexible.

edited Oct 19 '12 at 07:10

answered Oct 19 '12 at 06:53

GolezTrol

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can u give a simple example on how can i implement this if i were too display 5 items? Thank you :) – thenewbie Oct 19 '12 at 07:02
It doesn't matter how many items. Your function is called for each row separately. – GolezTrol Oct 19 '12 at 07:09
I've modified the loop, so you can return false to stop processing the dataset. – GolezTrol Oct 19 '12 at 07:13
PS: Stop using mysql_* use PDO or mysqli_* – GolezTrol Oct 19 '12 at 07:14
Thank you :). Do you have a basic instructions how to use it? – thenewbie Oct 19 '12 at 07:21
Hi. I tried your code and works great. although i have an error using mysqli.So i just replace it with mysql. I thinnk the problem is that the connection is not mysqli thats why i have an error. Beside that its great. Thank you again. – thenewbie Oct 19 '12 at 07:38

score 1 · Answer 3 · answered Oct 19 '12 at 06:49

1

No, it isn't.

You can return a function to does nothing but run a loop, but you can't return the loop itself.

answered Oct 19 '12 at 06:49

Quentin

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score 1 · Answer 4 · answered Oct 19 '12 at 06:49

1

No.

You could, for instance, return an anonymous function which may contain a loop, but you can only return values from functions, not language constructs.

answered Oct 19 '12 at 06:49

deceze

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ppeterka · Answer 5 · 2012-10-19T06:58:56.443

You should turn it inside out!

Instead of returning the loop, you could do it this way using Variable functions :

function myloop($sql, $myFunction){ 
    $query = mysql_query($sql);  
    while(mysql_fetch_assoc($query)) {
        $myFunction($result);
    }

} 


function doSomethingWithTheResult($result) {
   echo $result; // just to have something here...
}

//now the usage:
myloop("SELECT 1", 'doSomethingWithTheResult');

With a squint, this is similar to the concept of the Template method OOP design pattern.

BugFinder · Answer 6 · 2012-10-19T07:12:24.227

1

No, but you could do

function loopdate($sql,$code)
{
 $query=mysql_query($sql)
 while (mysql_fetch_assoc($query))
 {
  eval($code);
 }
}

However - eval is rediculously dangerous its really really discouraged.

function loopdate($sql,$function)
{
 $query=mysql_query($sql)
 while ($data=mysql_fetch_assoc($query))
 {
  $function($data);
 }
}

would be better.

myfunc($data)
{
 foreach ($data as $key->$value)
 {
  print "<tr><td>".$key."<td><td>".$value."</td></tr>\n";
 }
}

So you can call

loopdate("select * from mytable","myfunc");

edited Oct 19 '12 at 07:12

answered Oct 19 '12 at 06:53

BugFinder

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Thanks. BTW how can implement this if i were to display 10 or 5 items? :) – thenewbie Oct 19 '12 at 07:04

score 0 · Answer 7 · answered Feb 15 '13 at 18:25

In PHP 5.5+ it is possible, using the yield keyword instead of return (this is called a generator):

function myloop($sql) {
    $query = mysql_query($sql);
    while (($row = mysql_fetch_assoc($query))) {
        yield $row;
    }
}

foreach (myloop('SELECT * FROM foo') as $row) {
    // do something with $row
}

This is not much different from what you could do with iterators in older PHP, but the code is much cleaner.

Return a loop in function php

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