As of the 1.19 release, Dart supports an optional mode, called strong mode , that supports stronger static typing. Strong mode helps you find bugs sooner and contributes to making Dart a sound language. To learn more about using strong mode to enable soundness, including the how, the why, and fixes for common problems you might encounter, see: Sound Dart How and why to write sound Dart code, and how to use strong mode to enable soundness. Sound Dart: FAQ A list of common questions for those who are interested in stronger static typing. Sound Dart: Fixing Common Problems How to fix errors and warnings you may encounter when writing sound Dart code.