As I understand, for static types, data types are known at compile-time and for dynamic types, data types are known/evaluated at run-time.

The Dart document (https://dart.dev/faq#q-is-dart-a-statically-typed-language) says that dart is a statically typed language -

Q. Is Dart a statically typed language?
Yes, Dart 2 is statically typed. For more information, read about Dart’s type system.

With its combination of static and runtime checks, Dart has a sound type system, which guarantees that an expression of one type cannot produce a value of another type. No surprises!

Even with type-safe Dart, you can annotate any variable with dynamic if you need the flexibility of a dynamic language. The dynamic type itself is static but can contain any type at runtime. Of course, that removes many of the benefits of a type-safe language for that variable.

So then how are we able to assign a variable "dynamic" data type, which leaves the type evaluation at run-time?

CodePudding user response：

The short answer is that dynamic is a type on its own. It just moves the type-checking to runtime (as referred to in the text you quoted).

This lets you do things like final Map<String, dynamic> json = await fetchData();, which would not be possible otherwise.

Note that using the dynamic type is strongly discourage by Dart, specifically because of its runtime impact and lack of "staticness".

CodePudding user response：

The dynamic is one of the types.

So, if you want to use a dynamic variable, you have to cast it another types.