self | 易学教程

static:: vs. self:: - are there any downsides?

阅读更多关于 static:: vs. self:: - are there any downsides?

In this StackOverflow question I learned that self:: was not inheritance-aware where static:: was (in PHP). When it comes to defining a bunch of constants within a class, if you want to override those constants in a subclass to change default "behaviours", it becomes necessary to use static:: so that a method on the parent class that references the constant, honours the "override". In the 2 years since I asked that original question, I have started using static:: extensively, to the point that I rarely use self:: since self:: would appear to limit the extensibility of a class that uses

What does self do? [duplicate]

阅读更多关于 What does self do? [duplicate]

问题 This question already has answers here : Closed 8 years ago . Possible Duplicate: Python 'self' keyword Forgive me if this is an incredibly noobish question, but I never did understand self in Python. What does it do? And when I see things like def example(self, args): return self.something what do they do? I think I've seen args somewhere in a function too. Please explain in a simple way :P 回答1: It sounds like you've stumbled onto the object oriented features of Python. self is a reference

How to change self in a block like instance_eval method do?

阅读更多关于 How to change self in a block like instance_eval method do?

问题 instance_eval method change self in its block, eg: class D; end d = D.new d.instance_eval do puts self # print something like #<D:0x8a6d9f4>, not 'main'! end If we define a method ourself(or any other methods(other than instance_eval) which takes a block), when print self, we will get 'main', which is different from instance_eval method.eg: [1].each do |e| puts self # print 'main' end How can i define a method(which takes a block) like instance_eval? Thanks in advance. 回答1: You can write a

clickedButtonAtIndex in appdelegate is not called

阅读更多关于 clickedButtonAtIndex in appdelegate is not called

I am calling UIAlert with 2 buttons "Cancel" and "OK" in MyapplicationAppDelegate.m file , the alert is called but on tap of "Cancel" or "OK" button -(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex method is not called. I have added UIAlertViewDelegate in the MyapplicationAppDelegate.h file as below #import UIKit/UIKit.h @interface MyapplicationAppDelegate: NSObject UIApplicationDelegate,UIAlertViewDelegate { .. } I want to know what else is required. I am not sure whether its your typo while posting the question but you should call the delegate within <..

Why does Array#each return an array with the same elements?

阅读更多关于 Why does Array#each return an array with the same elements?

问题 I'm learning the details of how each works in ruby, and I tried out the following line of code: p [1,2,3,4,5].each { |element| el } And the result is an array of [1,2,3,4,5] But I don't think I fully understand why. Why is the return value of each the same array? Doesn't each just provide a method for iterating? Or is it just common practice for the each method to return the original value? 回答1: Array#each returns the [array] object it was invoked upon: the result of the block is discarded .

Lua: colon notation, 'self' and function definition vs. call

阅读更多关于 Lua: colon notation, 'self' and function definition vs. call

I'm getting terribly confused by the colon notation used when defining/calling Lua functions. I thought I'd got my head round it until I saw this piece of code: function string.PatternSafe( str ) return ( str:gsub( ".", pattern_escape_replacements ) ); end function string.Trim( s, char ) if char then char = char:PatternSafe() else char = "%s" end return string.match( s, "^" .. char .. "*(.-)" .. char .. "*$" ) or s end What's confusing me here is that string.PatternSafe() doesn't reference 'self' anywhere, yet the code seems to work. I've also seen some scripts that use colon notation when

iOS First Application “self.userName = textField.text”. When to use self

阅读更多关于 iOS First Application “self.userName = textField.text”. When to use self

问题 Here is a code snippet from Apple's "Your First iOS Application" document. - (IBAction)changeGreeting:(id)sender { self.userName = textField.text; NSString *nameString = self.userName; if ([nameString length] == 0) { nameString = @"World"; } NSString *greeting = [[NSString alloc] initWithFormat:@"Hello, %@!", nameString]; label.text = greeting; [greeting release]; } I understand that self.username calls the synthesized set method (important since it has a copy flag). Why is textField.text and

Java “self” (static) reference

阅读更多关于 Java “self” (static) reference

I am looking for a "self" reference to the current class in JAVA in a static context manner like in PHP Scope Resolution Operator ? Solution: Break out of scope? BEWARE, this is compared to a static definition really slow (by factor 300): static Logger LOG = LoggerFactory.getLogger(new RuntimeException().getStackTrace()[0].getClassName()); The old-fashioned way would be: static Logger LOG = LoggerFactory.getLogger(<Classname>.class.getName()); Are there any alternatives? I'm looking for a way to put the logger definition in an abstract class. The logger should determine the class it's being

how to use a Python function with keyword “self” in arguments

阅读更多关于 how to use a Python function with keyword “self” in arguments

问题 i have a function that retrieve a list of stores in Python this functions is called : class LeclercScraper(BaseScraper): """ This class allows scraping of Leclerc Drive website. It is the entry point for dataretrieval. """ def __init__(self): LeclercDatabaseHelper = LeclercParser super(LeclercScraper, self).__init__('http://www.leclercdrive.fr/', LeclercCrawler, LeclercParser, LeclercDatabaseHelper) def get_list_stores(self, code): """ This method gets a list of stores given an area code

What is the meaning of 'self' and 'init' expressions in Python? [closed]

阅读更多关于 What is the meaning of 'self' and '__init__' expressions in Python? [closed]

I don't understand what these are used for, particularly the self argument? Could some please explain this to me and why on earth you would want to pass this in? Also, I've always thought __init__ was for 'initialisation', but it didn't occur to me that I've never had to put anything in here before. Could someone give me an easy example? edit: i just get so confused everytime i see self being passed into a function, or something of the like. self is the object you're calling the method on. It's a bit like this in Java. __init__ is called on each object when it is created to initialise it. It's