Professional Dart: code generation, idioms and Flutter interview questions

Questions with model answers

What each question tests, the first step of a good answer and the follow-ups to expect.

1. Mid to senior

   A teammate ports a Java codebase to Dart and keeps every Gang-of-Four pattern as its own class hierarchy: a Strategy interface with a subclass per rule, a Subject and Observer, a State base class. Which would you simplify, and how do you explain the Dart version?

   What it tests

   Whether the candidate maps patterns to language features (function types, Stream, sealed classes) and keeps a class only when it earns one.

   First step

   Go pattern by pattern and ask what varies. If it is one behaviour, a function type replaces the hierarchy; if it is a fixed set of shapes with data, a sealed class does.

   Follow-ups

   • Which patterns still deserve a class or an interface in Dart?
   • How do you keep the simpler version readable for the Java developers on the team?
   • When is keeping the classic form the right call?

   From the lesson Idiomatic Dart: Effective Dart and patterns

   Model answer · Pro Model answer, Pro. Model answers open with any pass; prices are in the notice on this page.

   Opening the model answers with your pass…

   Model answers open with any MySmartCoPilot pass.

   • Pro pass · 1 week · ₹79 · $2.99
   • 30 days · ₹179 · $5.99
   • 1 year · ₹1,699 · $45

   One payment; nothing renews unless you choose to. The price shown is the total you pay: no fees or charges are added at checkout.

   Choose a passI have a licence key

   It also opens every other in-depth part in Learn and every Pro tool. Sales are final, except where the law gives you a right to withdraw, for example in the EU and the UK (refund policy).

   In the answer:

   • Model answer
   • Follow-up answers
   • Common mistakes
   • Rubric
   • Variants
   • about 3 minutes

2. Mid to senior

   A service parses JSON into Map<String, dynamic> and passes those maps deep into the code, reading fields as dynamic everywhere. Bugs show up only in production. What is wrong, by Effective Dart, and how do you change it?

   What it tests

   Whether the candidate knows dynamic turns off static checks, decodes once into typed classes at the edge, and validates untrusted input.

   First step

   Find where untrusted data enters and turn it into typed objects there, so the rest of the code works with checked types instead of dynamic.

   Follow-ups

   • What exactly does dynamic do that Object? does not?
   • Where do you validate the values, not just the types?
   • How does this also help performance?

   From the lesson Idiomatic Dart: Effective Dart and patterns

   Model answer · Pro Model answer, Pro.

   In the answer:

   • Model answer
   • Follow-up answers
   • Common mistakes
   • Rubric
   • Variants
   • about 3 minutes

3. Mid to staff

   A screen's state is a mutable class with nullable fields for loading, data and error, and bugs come from fields that disagree, such as data set while an error is also set. Redesign the state the Dart way and say what it prevents.

   What it tests

   Whether the candidate uses a sealed class with an exhaustive switch and immutable states, and explains the bugs it rules out.

   First step

   List the states the screen can really be in, make each a class under one sealed type, and give each only the data it needs.

   Follow-ups

   • What does the compiler now catch that it could not before?
   • How do immutable states help when the UI rebuilds?
   • Where do records fit, and where do they not?

   From the lesson Idiomatic Dart: Effective Dart and patterns

   Model answer · Pro Model answer, Pro.

   In the answer:

   • Model answer
   • Follow-up answers
   • Common mistakes
   • Rubric
   • Variants
   • about 3 minutes