Flutter Prague #5

What does the following code do in Flutter?

• Creates a container with a width of 100, a height of 200 and a blue color

• Causes a compilation error

• Creates an empty widget without any effect

• Throws a runtime exception

What is the difference between final x = ...; and late final x = ...; in Dart?

• final requires immediate initialization, while late final allows initialization only on first use if the value is not assigned immediately

• late final cannot be initialized on declaration

• late final must be initialized explicitly by a function

• late final allows you to change the value once, while final does not

What happens when you call setState() within StatelessWidget?

• Causes a runtime or compilation error because StatelessWidget does not have a setState method

• Revives the widget because all widgets can have a state

• It does nothing because StatelessWidget has no state

• Forces Flutter to rebuild the widget tree

Consider the following code:

• The code fails to compile

• The code runs successfully

• The code compiles, but it throws a runtime exception

Answer explanation

Feature: Statically checked declaration-site variance
https://github.com/dart-lang/language/issues/524

covariance: safe for reading (current Dart)

contravariance: safe for writing

invariance: safe for both reading and writing

Consider the following code, after calling foo() :

• It prints "Caught an error: Exception: oopsie"

• Throws a runtime exception

• The code does not compile

Consider the following code, after calling foo() :

• It prints "Caught an error: Exception: oopsie"

• Throws a runtime exception

• The code does not compile