Key-preserving salary-increasing sorting
Array
(
    [spider] => Acme\Employee Object
        (
            [id:Acme\Employee:private] => 3
            [name] => spiderman
            [salary:protected] => 0.82
            [age:Acme\Employee:private] => 50
        )

    [bat] => Acme\Employee Object
        (
            [id:Acme\Employee:private] => 2
            [name] => batman
            [salary:protected] => 1
            [age:Acme\Employee:private] => 73
        )

    [super] => Acme\Employee Object
        (
            [id:Acme\Employee:private] => 1
            [name] => superman
            [salary:protected] => 1.27
            [age:Acme\Employee:private] => 80
        )

)

Non-key-preserving salary-increasing sorting
Array
(
    [0] => Acme\Employee Object
        (
            [id:Acme\Employee:private] => 3
            [name] => spiderman
            [salary:protected] => 0.82
            [age:Acme\Employee:private] => 50
        )

    [1] => Acme\Employee Object
        (
            [id:Acme\Employee:private] => 2
            [name] => batman
            [salary:protected] => 1
            [age:Acme\Employee:private] => 73
        )

    [2] => Acme\Employee Object
        (
            [id:Acme\Employee:private] => 1
            [name] => superman
            [salary:protected] => 1.27
            [age:Acme\Employee:private] => 80
        )

)