问题
What does external mean in Dart? For example: external DateTime._now();
I'm new to Dart, I can't find documentation for external, so can you give an example to help explain？
回答1:
9.4 External Functions
An external function is a function whose body is provided separately from its
declaration. An external function may be a top-level function (17), a method
The body of the function is defined somewhere else.
As far as I know this is used to fix different implementations for Dart VM in the browser and Dart VM on the Server.
回答2:
When we make an external function inside a class like toString()
external String toString();
means this function is abstract and the child of the parent class will add the function body, that's because in Dart we only can make an abstract class.
Summary:
external function = abstract function in not abstract classes
来源：https://stackoverflow.com/questions/24929659/what-does-external-mean-in-dart