Avoid inheritance of class in Dart
dart
Solution
Not directly, no.
You could write a class with private constructors and access them via static methods:
class MyFinalClass {
MyFinalClass._ctor1() {}
MyFinalClass._ctor2(String param1, String param2) {}
static MyFinalClass getInstance() {
return new MyFinalClass._ctor1();
}
static MyFinalClass getInstanceWithParams(String param1, String param2) {
return new MyFinalClass._ctor2(param1, param2);
}
}
But this has multiple problems:
- Classes inside the same library can still subclass it - visibility in Dart applies to libraries, not single classes.
- It's a lot of code, scaling with the amount of constructors.
- It introduces lots of static methods, which all have to be named differently.
- And of course, you can't instantiate the class outside its library with the `new` keyword.
- This only prevents extension of a class. Implementing the "final" class is still possible.
Ultimately, these are quite a few drawbacks for this feature. It's up to you to decide if it is really worth it.
EDIT
Contrary to what I have written before, factory constructors would also work, eliminating the "unable to instantiate with `new` keyword" drawback.
class MyFinalClass {
factory MyFinalClass.ctor1() {}
factory MyFinalClass.ctor2(String param1, String param2) {}
void method1() {}
void method2() {}
}
Also, to illustrate why the ability to implement the not-so-final class is a big problem:
class Sub implements MyFinalClass {
MyFinalClass _d;
Sub.ctor1() {
_d = new MyFinalClass.ctor1();
}
Sub.ctor2(String p1, String p2) {
_d = new MyFinalClass.ctor2(p1,p2);
}
void method1() => _d.method1();
void method2() {
// do something completely different
}
}
This pseudo-subclassing would work with the static method variant as well.
Problem
Is there a way to avoid inheritance in Dart? I'm looking for something like ``` final class MyJavaClass { ... } ```