public/subjects/mobile-dev/named-optional-sum

Named Optional Sum

Instructions

Write a function named namedOptionalSum, that accepts named parameters first, second and third. It returns the sum of its parameters.

Absent parameters should be considered as 0.

Named parameters

In Dart you can declare functions that require explicit naming for arguments. Compare the following:

void someFunction(bool bold, bool hidden) {...}

someFunction(true, false);

void someFunction({bool? bold, bool? hidden}) {...}

someFunction(bold: true, hidden: false);

This way you must specify the name of argument each time you call a function. You can also skip the parameter by simply not specifying its name and value.

What do you think the default value will be for parameters which are skipped?

Null safety

You might be wondering what the ? sign means in bool?.

Types in your code are non-nullable by default, meaning that variables can’t contain null unless you say they can. With null safety, your runtime null-dereference errors turn into edit-time analysis errors.

What happens if the argument of the function is optional and it is omitted? It should be null, but the Dart's null safety does not allow it, and you will get an error from the compiler. In order to let Dart's compiler understand that certain variables should be able to accept null, you must initialize primitives with a ?.

See null safety.