dirtydozen

II. One-trick-pony variables

Don’t ride it just once

Programming often requires you to store data in memory during code execution. This programmatic memory storage vehicle is called variable which also has a type defined. For example, variables can be string, integer, boolean types, plus tons more.

var foo = "foo";
var message = "My message sentence";
var age = 35;
var isActive = true;
var temperature = 36.6;

Using variables the right way is a fine balance, which you as programmer, need to strike between readable code and memory utilisation.

Let’s consider this code below which in isolation doesn’t look too bad, right?

var patient = new Patient();
var nurse = new Nurse();

// some additional code left out for brevity

var patientMorningTemperature = patient.Temperature;
nurse.RecordPatientTemperature(patientMorningTemperature);

Problem Statement

Now let’s consider slightly bigger piece of code where hopefully the magnitude of the problem will manifest itself.

var patient = new Patient();
var nurse = new Nurse();

// some additional code left out for brevity

var patientMorningTemperature = patient.Temperature;
nurse.RecordPatientTemperature(patientMorningTemperature);

// some additional code left out for brevity

patient.TakenParacetamol();

// some additional code left out for brevity

var patientAfternoonTemperature = patient.Temperature;
nurse.RecordPatientTemperature(patientAfternoonTemperature);

What stands out in this code is that we have a number of One-trick-pony variables defined for the same piece of data, the temperature: patientMorningTemperature [line 6] & patientAfternoonTemperature [line 15]. In addition, the temperature variables are then simply passed to a function for Nurse to record [lines 7, 16] and are never re-used anywhere else in the code execution.

Is there any benefit of storing temperature in both patientMorningTemperature and patientAfternoonTemperature variables?

How about if this data was much bigger, perhaps a stream or data set?

Are you happy with the memory penalty associated with storing it twice?

Solution

Let’s re-use some of the data that is already available to us in code and prevent instantiating One-trick-pony variables unnecessarily. As result, the code will run faster and will be more readable.

Variation 1 - Reduction in variable use

var patient = new Patient();
var nurse = new Nurse();
var temperature = patient.Temperature;

// some additional code left out for brevity

nurse.RecordPatientTemperature(temperature);

// some additional code left out for brevity

patient.TakenParacetamol();

// some additional code left out for brevity

temperature = patient.Temperature;

// some additional code left out for brevity

nurse.RecordPatientTemperature(temperature);

With the code changes above, we’ve re-used the temperature variable [line 3] more than once [lines 7, 15, 19], so it’s no longer a One-trick-pony unnecessarily. And sometimes that’s all you might need to do - all depending on what’s happening in between the some additional code left out for brevity sections [lines 5, 9, 13, 17].

Variation 2 - No variable use

var patient = new Patient();
var nurse = new Nurse();

// some additional code left out for brevity

nurse.RecordPatientTemperature(patient.Temperature);

// some additional code left out for brevity

patient.TakenParacetamol();

// some additional code left out for brevity

nurse.RecordPatientTemperature(patient.Temperature);

Consider code above now where we’ve gotten rid of the One-trick-pony variables altogether because we’ve realised these were not required for anything else other than passing a piece of information which was already defined and set on the Patient object. Therefore, we could acquire the temperature directly form patient.Temperature attribute [lines 6, 14].

Summary

I understand that assigning a small variable seems innocent at the time of coding and sometimes doing so might be required for clarity.

However, try not to get into a bad habit of creating too many of these One-trick-pony variables unnecessarily...