PHP - 局部变量更改会导致全局更改

Question

I am stuck, I can't find any reference to this problem. It shouldn't be happening. The global variable $assignmentInfo is passed into the function, manipulated, and returned as a different variable.

BUT, the local manipulations within the function are propagated to the global variable, so that the next time the function gets called, $assignmentInfo has been changed. I want to pass in the same, unchanging version of $assignmentInfo each time I call the function.

Any suggestions?

function studentScores($submissionInfo, $assignmentInfo){
    //********************************** Add submission data to assignment data ****************************************************************************
    foreach($assignmentInfo as $assignmentGroup){
        foreach($assignmentGroup->assignments as $assignment){
            foreach($submissionInfo as $submission){
                if(isset($assignment->id) and isset($submission->assignment_id) and $assignment->id == $submission->assignment_id){
                    if (isset($submission->score)){$assignment->score = $submission->score;}
                    if (isset($submission->submitted_at)){$assignment->submitted_at = $submission->submitted_at;}
                    if (isset($submission->workflow_state)){$assignment->workflow_state = $submission->workflow_state;}
                    break;
                }
            }       
        }
    }
    $studentScores = $assignmentInfo;
    return $studentScores;
}

$studentScores = studentScores($submissionInfo->submissions, $assignmentInfo);