> Hello, > > This is the second time I've tried to post to the list, but I haven't > seen my first attempt show up in the vala-list archive yet, so I thought > I would resend, just in case. > > I'm still learning my way around vala so I may be doing something wrong, > but according to the docs at https://wiki.gnome.org/Vala/Manual/Classes: > > * Class members are shared between all instances of a class. They can > be accessed without an instance of the class, and class methods will > execute in the scope of the class.
I'll mark some points: Class members are sharing ACCESS between all instances of a class. They can be accessed without an instance of the class(BUT HAVE TO SPECIFY ANOTHER INSTANCE TO GET TO), and class methods will execute in the scope of the class(WITH A GIVEN INSTANCE). There's an only one exception to my marking - static members. Static members belong to the class, not to the instance, and therefore its value is "shared" between all instances and the class. More about static vs non-static members(in OOP): http://www.daniweb.com/software-development/csharp/threads/96978/static-vs-non-static-methods > > This does not appear to be the case. In the following example I cannot > access the prop method of the Parent or Child classes without > instantiating an instance of those classes. > > public class Parent : Object { > protected class int _prop; > public class int prop() { return _prop; } > class construct { > _prop = 0; > } > } > > public class Child : Parent { > class construct { > _prop = 1; > } > } > > Parent p = new Parent(); > print ("Parent.prop: %d\n", p.prop()); // Works as expected > print ("Parent.prop: %d\n", Parent.prop()); // error: Access to > instance member `Parent.prop' denied > > Child c = new Child(); > print ("Child.prop: %d\n", c.prop()); // Works as expected > print ("Child.prop: %d\n", Child.prop()); // error: The name `prop' > does not exist in the context of `Child' > > Is this the desired behavior or are class methods, suppose to only be > accessible from class instances? > > Kind Regards, > > Tom > This is desirable behavior. Notice that it works fine when calling method "prop" by instance. When you call this method by a class name, it fails, since ONLY static method are allowed to be called by a class name. Child.prop() would fail even if prop() is static, since the method belongs to Parent, and not to Child. > I believe it's a bug in the compiler. It's non-sense to require an instance > when those are class-level instances. Sorry, but I don't understand you. Why it's a bug in compiler? > However as a workaround you can use static fields. You can still initialize > them with class construct { } or static construct { }. So why don't just do this? > Also if you were thinking of overriding a protected class field, I hardly > believe that's implemented (there's a bug somewhere about that) No I checked this in the past, Vala doesn't support this. It could theoretically can be possible by register this with GObject class struct, but it's a source for ABI breaks. Better to implicate this with a virtual static get method. I do accept that this could be a nice feature. Tal _______________________________________________ vala-list mailing list vala-list@gnome.org https://mail.gnome.org/mailman/listinfo/vala-list
