class-method

问题 Foo = Class.new Foo.class_eval do def class_bar "class_bar" end end Foo.instance_eval do def instance_bar "instance_bar" end end Foo.class_bar #=> undefined method ‘class_bar’ for Foo:Class Foo.new.class_bar #=> "class_bar" Foo.instance_bar #=> "instance_bar" Foo.new.instance_bar #=> undefined method ‘instance_bar’ for #<Foo:0x7dce8> Just based on the name of the methods, I would expect class_eval to allow you to add a class method to Foo and instance_eval to allow you to add an instance

问题 I'm new to the new query interface of ActiveRecord so I'm still figuring things out. I was hoping someone could explain the difference between using a scope in an ActiveRecord model and just using a class method (ie self.some_method ) From what I can gather, a scope is always expected to return a relation, whereas a class method doesn't necessarily have to. Is this true? For instance, I thought it would make sense to do something like: class Person scope :grouped_counts, group(:name).count

问题 Apart from the standard [[MyClass alloc] init] pattern, some objects are built from static methods like MyClass *obj = [MyClass classWithString:@"blabla"] According to widespread memory management guides (including Apple's), you're only responsible for releasing the objects that you alloc . Can anyone provide me with a template for such methods? How do you return the allocated object ( [self alloc]; return self; , perhaps)? How do you make sure that it will be released? 回答1: They are class

问题 This is an academic question, more than a practical one. I'm trying to delve into the foundations of Python, and I wonder: could I implement the staticmethod and classmethod decorators in pure Python if I wanted to? For staticmethod maybe I could keep a reference to the original function and call it omitting the first argument? For classmethod maybe I could keep a reference to the original function and call it passing the type of the first argument, rather than the argument itself? (How would

问题 If I call a method on a rails active model method like so: class Foo < ActiveRecord::Base end Foo.first I'll get back the first active record. I don't have to instantiate the class. But if I create my own class and call a method, I get an exception: class Person < ActiveRecord::Base def greeting 'hello' end end Person.greeting #EXCEPTION: undefined method `greeting' for Person:Class How can I make that problem go away? 回答1: There are several kinds of methods. The two most important ones are:

问题 I have the following Python metaclass that adds a deco_with_args decorator to each class: def deco_with_args(baz): def decorator(func): ... return func return decorator class Foo(type): def __prepare__(name, bases): return {'deco_with_args': deco_with_args} This allows me to use the decorator like this: class Bar(metaclass=Foo): @deco_with_args('baz') def some_function(self): ... How do I make the deco_with_args decorator behave like an @classmethod so that I can access the Bar class (or

问题 I havea Utility class that uses class methods. I am trying to refer to self in the class method but can't. I was wondering how would I declare the following in a class method: [MRProgressOverlayView showOverlayAddedTo:self.window animated:YES]; self.window it says member reference type struct objc_class *' is a pointer; maybe you meant to use '->' Another problem that relates to not being able to call self is how would I refer to a declared @property in my .h in a class method in my .m . Here

问题 I have to use some Python library which contains file with various utilities: classes and methods. One of these methods is defined in the following way (I cannot put whole code): @classmethod def do_something(cls, args=None, **kwargs): but this declaration is outside any class. How can I get access to this method? Calling by do_something(myClass) gives an error: TypeError: 'classmethod' object is not callable . What is the purpose of creating classmethods outside classes? 回答1: The decorator

问题 Example def Object.const_missing(name) puts self.class end class A; end A::B # => Class How can I get A in Object#const_missing ? 回答1: def Object.const_missing(name) puts self end 来源： https://stackoverflow.com/questions/3314108/if-i-define-a-class-method-in-ruby-object-class-how-do-i-get-the-name-of-a-chil

问题 I was trying to override __str__ and __repr__ for class as shown in the code below. The new methods are called whenever I call the instance_method but the object calls for class_method remains the same (Please see the code snippet and the output below for clarity). Is there a way possible to override __str__ and __repr__ for @classmethod so that the value of cls can be changed? I have also tried adding __str__ and __repr__ as @classmethod but nothing changed. class Abc: def __init__(self,