using functions instead methods in SomethingRequest for validation

I would like to validate different variables by calling a special function in request in Laravel. How could I do it?

if ($this->function() == 'function1') {
     return [
                'firstName' => 'required|unique:networks,name|min:2',
            ];
} elseif ($this->function() == 'function2') {
     return [
                'lastName' => 'required|unique:networks,name|min:5'
            ];
}

via Chebli Mohamed