<h2>Original Instruments</h2>array(3) {
  [0]=>
  array(2) {
    ["instrument"]=>
    string(5) "Piano"
    ["price"]=>
    int(3000)
  }
  [1]=>
  array(2) {
    ["instrument"]=>
    string(6) "Guitar"
    ["price"]=>
    int(800)
  }
  [2]=>
  array(2) {
    ["instrument"]=>
    string(6) "Violin"
    ["price"]=>
    int(1500)
  }
}
<h2>After applyDiscount (Pass by Value)</h2>array(3) {
  [0]=>
  array(2) {
    ["instrument"]=>
    string(5) "Piano"
    ["price"]=>
    float(2700)
  }
  [1]=>
  array(2) {
    ["instrument"]=>
    string(6) "Guitar"
    ["price"]=>
    float(720)
  }
  [2]=>
  array(2) {
    ["instrument"]=>
    string(6) "Violin"
    ["price"]=>
    float(1350)
  }
}
<h2>Original Instruments After Pass by Value</h2>array(3) {
  [0]=>
  array(2) {
    ["instrument"]=>
    string(5) "Piano"
    ["price"]=>
    int(3000)
  }
  [1]=>
  array(2) {
    ["instrument"]=>
    string(6) "Guitar"
    ["price"]=>
    int(800)
  }
  [2]=>
  array(2) {
    ["instrument"]=>
    string(6) "Violin"
    ["price"]=>
    int(1500)
  }
}
<h2>After applyDiscountByReference (Pass by Reference)</h2>array(3) {
  [0]=>
  array(2) {
    ["instrument"]=>
    string(5) "Piano"
    ["price"]=>
    float(2700)
  }
  [1]=>
  array(2) {
    ["instrument"]=>
    string(6) "Guitar"
    ["price"]=>
    float(720)
  }
  [2]=>
  array(2) {
    ["instrument"]=>
    string(6) "Violin"
    ["price"]=>
    float(1350)
  }
}