Difference between Object, Dynamic and Var in Dart?

Question

There is a discussion about dynamic and var before null-safety. Then what's the Object? between each of them?

1. Is Object? == dynamic?
2. How about var? and dynamic??
3. Any difference between dynamic? and dynamic?

I see the official document about null-safety, but can't find the related topic.

Answer 1

1. dynamic is a special type that disables static type-checking. You can attempt to call any method on a dynamic type. If the object turns out not to have such a method, then it will result in a runtime failure instead of a compile-time one.

   Object? is a base type suitable for referencing any object, including null. Unlike dynamic, it is statically type-checked, so you would get compile-time failures if you attempt to call most methods on it without explicitly checking the runtime type or without performing a cast.

2. var? is not valid syntax. var is not a type; it declares a variable without explicitly specifying a type, allowing the type to be inferred.

   dynamic? is valid but is redundant. (See #3.)

3. Variables of type dynamic can already include null, so adding a ? to make it nullable is redundant. The Dart analyzer will tell you so.