Split declaration and initialisation in class, C++

Question

I started out with a piece of code that both declares and initialises two objects from 3rd party libraries in one line (see below). That worked just fine.

#include <OneWire.h>
#include <DallasTemperature.h>

const int gpioPin = 0;
OneWire oneWire(gpioPin);
DallasTemperature sensors(&oneWire);

I then wanted to wrap it in a class and initialise oneWire and sensors when the class is initialised. So I came up with this:

#include <OneWire.h>
#include <DallasTemperature.h>

class TemperatureSensor
{
private:
  OneWire oneWire;
  DallasTemperature sensors;

public:
  TemperatureSensor(int gpioPin);
};

TemperatureSensor::TemperatureSensor(int gpioPin)
{
  oneWire(gpioPin);
  sensors(&oneWire);
}

Which throws the error call of an object of a class type without appropriate operator() or conversion functions to pointer-to-function type. So I guess I can't initialise an object like that when the declaration is already made. Any help is much appreciated.