Programming in Dart: Fundamentals

Apr 26 2022 · Dart 2.15, DartPad, DartPad

Part 2: Introducing Collections & Null Safety

13. Understand Null Safety

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Previous episode: 12. Challenge: Work with Lists Next episode: 14. Create a Conditional List

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In 2021, Dart was upgraded with a huge feature that would affect every single line of Dart. And that was null safety. It was a huge upgrade and it really comes into play when working with collections. So what is null safety? What is being null? Null means the absence of a value. Lets say you are teacher, writing some code to make correcting grades easier for you. You may create a quiz but how do you know that a student has actually taken the quiz? Well, you could set the quiz value to zero, but that’s an actual grade. So you may next choose a negative number like negative one but what if your data store doesn’t accept negative numbers? After all, you can’t actually have a negative grade? You could solve this problem in a variety of ways but with null, it’s already solved for you.

var grades = List<int?>.empty(growable: true);

grades.add(100);
grades.add(null);
grades.add(84);

var total = 0;

var firstTest = grades[0];

total += firstTest;

if (firstTest != null) {
    total += firstTest;
} 

total += grades[1] ?? 0;

total += grades[2]!; 

var average = total / grades.length;
print('The average is $average');