Named parameters

When calling a function, you can specify named parameters using paramName: value.

When defining a function, use {param1, param2, …} to specify named parameters.

Although named parameters are a kind of optional parameter, you can annotate them with @required to indicate that the parameter is mandatory — that users must provide a value for the parameter.

If someone tries to create a Scrollbar without specifying the child argument, then the analyzer reports an issue.

To use the @required annotation, depend on the meta package and import package:meta/meta.dart.