Created arrays in PHP 5.6 with [] work, but in PHP 7.1 give fatal error

In PHP 5.6 this works fine, but in PHP 7.1 it gives Fatal error: Uncaught Error: [] operator not supported for strings

$result->execute();
$result->bind_result($id, $name);   
while($result->fetch()){
    $datos[]=array(
        $id => $name
    );
}

As of PHP 7.1, when you access a non-array variable (in this case a string) like an array, a fatal error will be thrown.

Initialize the array first, with $datos = [];. This will overwrite anything you have set earlier, and explicitly set this variable as an array:

$result->execute();
$result->bind_result($id, $name);
$datos = [];
while($result->fetch()){
    $datos[]=array(
        $id => $name
    );
}

If you're trying to create an array of $id => $name, the following code should work:

$result->execute();
$result->bind_result($id, $name);
$datos = [];
while($result->fetch()){
    $datos[ $id ] = $name;
}