How can I make this iterative conditional within the Loop work via function?

Question

I want an element to appear within the Loop, but only at certain points. I can supply the condition - in the form of a "flag" that gets set when the condition is fulfilled, preventing further iteration - directly in a template file, and it works, but when I produce the identical logic via function the flag does not seem to be set.

In other words - providing a simplified (the simplest!) case - the following works - CASE 1:

while( have_posts() ) : the_post();

if ( $flag < 1 ) {
    echo 'Flag worked!';
    $flag = 1;
}

/* all of the code producing a post */

endwhile;

The above works as expected: "Flag worked!" appears once and never again.

If, however - CASE 2 - I write a function, like so, and add it to the theme functions.php...

function flag_it() {
   if ( $flag < 1 ) {
       echo 'Flag worked!';
       $flag = 1;
   }
}

...and then place it in the exact same place as the first code, like so:

while( have_posts() ) : the_post(); 

flag_it();

/* all of the code producing a post */

endwhile;

The words "Flag worked" are turned into a lie, and appear before every post in the loop. In other words, the $flag value is not assessed by the if conditional, or the value of $flag continues to be treated as NULL ( so, "$flag < 1" remains true).

I've tried variations on the theme - with TRUE v FALSE, returned variables, value declared as 0, etc. - but none works, or, if it did!, would answer the basic question: Why does case 1 work, but not case 2, and is there any way to make case 2 or something like it - flagged condition supplied via function - work?

Answer 1

The problem is that whenever you call flag_it() there's no $flag available, so it's always going to result in "flag worked". Try using a static variable instead:

function flag_it() {
    static $flag;
    if ( isset( $flag ) )
        return;

    $flag = true;
    echo 'Flag worked!';
}

Note that no matter how many times you call this function in a run, it will always echo just once. If you want to reset the counter you'll need to change it to accept some sort of $reset argument.

You can read more about variable scopes in PHP here: http://php.net/manual/en/language.variables.scope.php