I’m trying to pass an object to a function in PHP to split a long function. The first example is the working way with the long funcion:

public function import() {
    $this->importSections();
}
public function importSections() {
    $reader = new PhpOfficePhpSpreadsheetReaderXlsx();
    $spreadsheet = $reader->load($this->_file);
    $sheet = $spreadsheet->getSheetByName('Sections');
    $highestRow = $sheet->getHighestDataRow(); // <- this works
    // ... //
}

However, I get the Error Call to a member function getHighestDataRow() on string on the above marked line if I try to split the function and pass the sheet like this:

public function import() {
    $reader = new PhpOfficePhpSpreadsheetReaderXlsx();
    $spreadsheet = $reader->load($this->_file);
    $sheet = $spreadsheet->getSheetByName('Sections');
    $this->importSections($sheet);
}
public function importSections($sheet) {
    $highestRow = $sheet->getHighestDataRow(); // <- Error
    // ... //
}

And if I explicitly pass it by reference like this..:

public function import() {
    $reader = new PhpOfficePhpSpreadsheetReaderXlsx();
    $spreadsheet = $reader->load($this->_file);
    $sheet = $spreadsheet->getSheetByName('Sections');
    $this->importSections($sheet);
}
public function importSections(&$sheet) {
    $highestRow = $sheet->getHighestDataRow(); // <- Error
    // ... //
}

…I get the error Argument #1 ($sheet) could not be passed by reference.

Can someone please explain what is going on here?