How to create an array of objects in PHP dynamically

There is no way to write object literals in PHP like you can in JavaScript or other languages.

The easiest way you can do this in PHP is using type casting

// associative array
$arr = ["a" => 1, "b" => 2, "c" => 3, "d" => 4];

// cast as object
$obj = (object) $arr;

// Or you could do it all in one line
$obj = (object) ["a" => 1, "b" => 2, "c" => 3, "d" => 4];

Check it out

echo $obj->a; // 1
echo $obj->b; // 2
echo $obj->c; // 3
echo $obj->d; // 4
echo json_encode($obj); // {"a":1,"b":2,"c":3,"d":4}

Your loop might look something like this

$objects = [];
for ($i=0; $i<4; $i++) {
  // i'll just makeup some values for a,b,c,d here since i don't know
  // how you are assigning them
  $objects[] = (object) [
    "a" => $i,
    "b" => $i * 2,
    "c" => $i * $i,
    "d" => rand()
  ];
}
print_r($objects);

Output

Array
(
    [0] => stdClass Object
        (
            [a] => 0
            [b] => 0
            [c] => 0
            [d] => 102971157
        )

    [1] => stdClass Object
        (
            [a] => 1
            [b] => 2
            [c] => 1
            [d] => 167903564
        )

    [2] => stdClass Object
        (
            [a] => 2
            [b] => 4
            [c] => 4
            [d] => 1894248447
        )

    [3] => stdClass Object
        (
            [a] => 3
            [b] => 6
            [c] => 9
            [d] => 929037839
        )

)

And the JSON output

[
  {"a":0,"b":0,"c":0,"d":102971157},
  {"a":1,"b":2,"c":1,"d":167903564},
  {"a":2,"b":4,"c":4,"d":1894248447},
  {"a":3,"b":6,"c":9,"d":929037839}
]

EDIT

how I could order my array by attribute b?

First create two reusable comparators

function ascendingComparator($a, $b) {
  if ($a > $b)      return 1;
  else if ($a < $b) return -1;
  else              return 0;
}

function descendingComparator($a, $b) {
  return -1 * ascendingComparator($a, $b);
}

Then use usort to pass the b property into the comparator

// sort ascending; lowest b value will be first in the array
usort($objects, function($x, $y) {
  return ascendingComparator($x->b, $y->b);
});
echo json_encode($objects);

// OR sort descending; highest b value will be first in the array
usort($objects, function($x, $y) {
  return descendingComparator($x->b, $y->b);
});
echo json_encode($objects);