Question

function foo()
{ echo 'function called'; }

Is it possible to do something like this:

onchange($a, foo);
$a = "foo"; // echoes 'function called'
$a = "bar"; // echoes 'function called'

Instead of:

$a = "foo";
foo();      // echoes 'function called'
$a = "bar";
foo();      // echoes 'function called'

Answer 1

Sort of. You can use what’s called a setter, a function designed to set a variable.

function setFoo ($value)
{
    echo 'in setFoo';
    return $value;
}

$a = setFoo('foo'); // echoes 'in setFoo'
echo $a; // echoes 'foo'
$a = setFoo('bar'); // echoes 'in setFoo'
echo $a; // echoes 'bar'