PHP: in-line default value for variables,

Use less code to do what you need.

You don't need to specify the variable again using the _?_:_ format.

echo $var?:"default";

Is the same as

echo $var?$var:"default";

Now as far as an empty check, you could use @ to mute notices, I'm not sure of the technical ramifications, but you're already doing your own checking while using this format:

echo @$non_existing_var?:"default";

Some examples:

<?php

    $nope = null;
    $yup = "hello";
    echo ($nope?:$yup) . "\n" ;
    echo ($yup?:$nope)  . "\n" ;

    $items = [ 'one', 'two', false, 'three', 'four', null ];

    foreach($items as $item):
        echo($item?:"default shown (".var_export($item,true).")")."\n";
    endforeach;

    echo(@$non_existing?:"default for non-existant variable!");

?>

Output:

$ php variabledefault.php
 hello
 hello
 one
 two
 default shown (false)
 three
 four
 default shown (NULL)
 default for non-existant variable!%