instance-variables

Since recent runtimes in iOS, we are able to define properties that will generate accessors for instance variables. From what I understand, it is not mandatory to declare the instance variable used since it will be automatically done for us. For example, if I write: @interface MyFirstClass @property (readonly, nonatomic) int size; @end and in the .m @implementation MyFirstClass @synthesize size; @end Then an instance variable named "size" will be added for me and a method called "-(int)size" will be implemented. The problem is that when I create a second class MySecondClass which is a subclass

I need something like this: @property (nonatomic, retain) int field[10][10]; but this code doesn't work. How to replace it? I need both setter and getter methods You can do it if you wrap the array in a struct. Structs are supported in @property notation (see CGRect bounds on CALayer, for example). First define your struct: typedef struct { int contents[10][10]; } TenByTenMatrix; Then, in your class interface, you can do: @property (assign) TenByTenMatrix field; Note that in this case, you can only get or set the whole array using the property. So you can't do self.field.contents[0][0] = 1;

I want a child class to inherit a class-level instance variable from its parent, but I can't seem to figure it out. Basically I'm looking for functionality like this: class Alpha class_instance_inheritable_accessor :foo # @foo = [1, 2, 3] end class Beta < Alpha @foo << 4 def self.bar @foo end end class Delta < Alpha @foo << 5 def self.bar @foo end end class Gamma < Beta @foo << 'a' def self.bar @foo end end And then I want this to output like this: > Alpha.bar # [1, 2, 3] > Beta.bar # [1, 2, 3, 4] > Delta.bar # [1, 2, 3, 5] > Gamma.bar # [1, 2, 3, 4, 'a'] Obviously, this code doesn't work.

I have a Ruby class. I want to get an instance variable from an argument to a method in that class. I can do get all of the instance variables as an array: self.instance_variables However, I want to get the instance variable named arg , specifically: class MyClass def get_instance_variable(arg) hash_of_instance_variables[arg] end end object.get_instance_variable('my_instance_var') How do I compute hash_of_instance_variables ? Yossi To create a hash of all instance variables you can use the following code: class Object def instance_variables_hash Hash[instance_variables.map { |name| [name,

Same in Ruby 1.8.7 and 1.9.2: $ irb ruby-1.8.7-p302 > foo.nil? NameError: undefined local variable or method `foo' for #<Object:0x3794c> from (irb):1 ruby-1.8.7-p302 > @bar.nil? => true ruby-1.8.7-p302 > @@wah.nil? NameError: uninitialized class variable @@wah in Object from (irb):3 why the instance variable treated differently than a local and class variable? In Ruby, most uninitialized or even non-existing variables evaluate to nil . This is true for local variables, instance variables and global variables: defined? foo #=> nil local_variables #=> [] if false foo = 42 end defined? foo #=>

I'm working on building an iOS 6 app. I have a class TDBeam which inherits from superclass TDWeapon . The superclass TDWeapon declares a @property in the TDWeapon.h file: @interface TDWeapon : UIView @property (nonatomic) int damage; @end I do not explicitly @synthesize the property, as I'm letting Xcode automatically do so. In the subclass TDBeam I override the getter in the TDBeam.m file: #import "TDBeam.h" @implementation TDBeam - (int)damage { return _damage; } @end Xcode auto-completes the getter method name, as expected. But when I attempt to reference the _damage instance variable

Is it possible to define properties that are only available to the class they are defined in, and that class's subclasses? Stated another way, is there a way to define protected properties? Technically, no. Properties are really just methods, and all methods are public. The way we "protect" methods in Objective-C is by not letting other people know about them. Practically, yes. You can define the properties in a class extension, and still @synthesize them in your main implementation block. This is possible by using a class extension (not category) that you include in the implementation files

I am creating a query builder class that will help in constructing a query for mongodb from URL params. I have never done much object oriented programming, or designed classes for consumption by people other than myself, besides using basic language constructs and using django's built in Models. So I have this QueryBuilder class class QueryHelper(): """ Help abstract out the problem of querying over vastly different dataschemas. """ def __init__(self, collection_name, field_name, params_dict): self.query_dict = {} self.params_dict = params_dict db = connection.get_db() self.collection = db

When using Objective-C properties can you stop creating instance variables altogether or do explicit instance variables (not the ones synthesized by the properties) still serve a purpose where properties would be inappropriate? can you stop creating instance variables altogether No, you can't (in a sense). What you can do is stop declaring them if you have properties. If you synthesize a property and you haven't declared the instvar, it will get declared for you, so you are creating an instance variable, just not explicitly. do they still serve a purpose where properties would be inappropriate