Can one declare a static method within an abstract class, in Dart?

class static dart abstract
cc young picture cc young · Dec 23, 2013 · Viewed 8.8k times · Source

In an abstract class, I wish to define static methods, but I'm having problems.

In this simple example

abstract class Main {
  static String get name;
  bool use( Element el );
}

class Sub extends Main {
  static String get name => 'testme';
  bool use( Element el ) => (el is Element);
}

I receive the error:

function body expected for method 'get:name' static String get name;

Is there a typo in the declaration, or are static methods incompatible with abstract classes?

Answer

Günter Zöchbauer picture Günter Zöchbauer · Dec 23, 2013

Dart doesn't inherit static methods to derived classes. So it makes no sense to create abstract static methods (without implementation).

If you want a static method in class Main you have to fully define it there and always call it like Main.name

== EDIT ==

I'm sure I read or heard some arguments from Gilad Bracha about it but can't find it now.

This behaviour is IMHO common mostly in statically typed languages (I don't know many dynamic languages). A static method is like a top level function where the class name just acts as a namespace. A static method has nothing to do with an instantiated object so inheritance is not applicable. In languages where static methods are 'inherited' this is just syntactic sugar. Dart likes to be more explicit here and to avoid confusion between instance methods and static methods (which actually are not methods but just functions because they don't act on an instance). This is not my primary domain, but hopefully may make some sense anyways ;-)

Related questions

in Dart, problems with static method when called from variable

have class Klass with static method fn1 class Klass { static String fn1() => 'hello'; } > Klass.fn1(); // hello but when Klass is assigned to a variable, calling the method fn1 fails var k = Klass; > k.fn1() // "Unhandled exception: Class …

Read More
Are static class variables possible in Python?

Is it possible to have static class variables or methods in Python? What syntax is required to do this?

Read More
When to use static classes in C#

Here's what MSDN has to say under When to Use Static Classes: static class CompanyInfo { public static string GetCompanyName() { return "CompanyName"; } public static string GetCompanyAddress() { return "CompanyAddress"; } //... } Use a static class as a unit of organization for methods not associated …

Read More