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  • Alternatives to the Singleton Design Pattern

    The Singleton Design Pattern is one of the simplest and most widely known design patterns in use in software development. However, despite its simplicity, it is very easy to get wrong and the consequences of its use even when properly implemented can outweigh its benefits. It turns out there are other ways to achieve the goals of the Singleton pattern which will often prove to be simpler, safer, and more maintainable.

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  • Red Dot Scope Makes Sighting In Long Lenses a Snap

    - by Jason Fitzpatrick
    If you’ve ever used a high power lens, you know how tricky it can be to sight a distant subject as the field of view through the lens is so tiny. This hack takes care of that problem by using a zero-magnification red dot rifle scope. Chris Malcolm enjoys photographing birds and other wildlife with high power lenses. The problem, when shooting with huge 500mm lens and other high power lenses, is that they’re practically telescopes and acquiring a fast moving target like a bird using a through-the-lens technique is very tricky. Malcolm’s solution hinges on mounting a zero-magnification red dot rifle scope in parallel with the lens. His mock up is a bit unpolished (although we can understand not wanting to run out and buy a brand new black scope just for the experiment) but works great to get him on target. Hit up the link below to read more about his build, how be created the rail mount for the scope, and why he opted to mount it to the barrel of the lens and not the hot shoe mount on the camera. 500mm Reflex Lens with Red Dot Sight [via DIY Photography] Make Your Own Windows 8 Start Button with Zero Memory Usage Reader Request: How To Repair Blurry Photos HTG Explains: What Can You Find in an Email Header?

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  • How do you create a non-Thread-based Guice custom Scope?

    - by Russ
    It seems that all Guice's out-of-the-box Scope implementations are inherently Thread-based (or ignore Threads entirely): Scopes.SINGLETON and Scopes.NO_SCOPE ignore Threads and are the edge cases: global scope and no scope. ServletScopes.REQUEST and ServletScopes.SESSION ultimately depend on retrieving scoped objects from a ThreadLocal<Context>. The retrieved Context holds a reference to the HttpServletRequest that holds a reference to the scoped objects stored as named attributes (where name is derived from com.google.inject.Key). Class SimpleScope from the custom scope Guice wiki also provides a per-Thread implementation using a ThreadLocal<Map<Key<?>, Object>> member variable. With that preamble, my question is this: how does one go about creating a non-Thread-based Scope? It seems that something that I can use to look up a Map<Key<?>, Object> is missing, as the only things passed in to Scope.scope() are a Key<T> and a Provider<T>. Thanks in advance for your time.

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  • php variable scope in oop

    - by mr o
    Hi, I wonder if anyone can help out here, I'm trying to understand how use an objects properties across multiple non class pages,but I can't seem to be able to get my head around everything i have tried so far. For example a class called person; class person { static $name; } but i have a number of different regular pages that want to utilize $name across the board. I have trying things like this; pageone.php include "person.php"; $names = new Person(); echo person::$name; names::$name='bob'; pagetwo.php include "person.php"; echo person::$name; I can work with classes to the extent I'm OK as long as I am creating new instances every page, but how can make the properties of one object available to all, like a shared variable ? Thanks

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  • python variable scope

    - by Oscar Reyes
    I'm teaching my self python and I was translating some sample class Student: def __init__( self, name, a,b,c ): self.name = name self.a = a self.b = b self.c = c def average(self): return ( a+b+c ) / 3.0 Which is pretty much my intended class definition Later in the main method I create an instance and call it a if __name__ == "__main__" : a = Student( "Oscar", 10, 10, 10 ) That's how I find out that the variable a declared in main is available to the method average and that to make that method work , I have to type self.a + self.b + self.c instead What's the rationale of this? I found related questions, but I don't really know if they are about the same

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  • Google's 'go' and scope/functions

    - by danwoods
    In one of the example servers given at golang.org: package main import ( "flag" "http" "io" "log" "template" ) var addr = flag.String("addr", ":1718", "http service address") // Q=17, R=18 var fmap = template.FormatterMap{ "html": template.HTMLFormatter, "url+html": UrlHtmlFormatter, } var templ = template.MustParse(templateStr, fmap) func main() { flag.Parse() http.Handle("/", http.HandlerFunc(QR)) err := http.ListenAndServe(*addr, nil) if err != nil { log.Exit("ListenAndServe:", err) } } func QR(c *http.Conn, req *http.Request) { templ.Execute(req.FormValue("s"), c) } func UrlHtmlFormatter(w io.Writer, v interface{}, fmt string) { template.HTMLEscape(w, []byte(http.URLEscape(v.(string)))) } const templateStr = ` <html> <head> <title>QR Link Generator</title> </head> <body> {.section @} <img src="http://chart.apis.google.com/chart?chs=300x300&cht=qr&choe=UTF- 8&chl={@|url+html}" /> <br> {@|html} <br> <br> {.end} <form action="/" name=f method="GET"><input maxLength=1024 size=70 name=s value="" title="Text to QR Encode"><input type=submit value="Show QR" name=qr> </form> </body> </html> ` Why is template.HTMLEscape(w, []byte(http.URLEscape(v.(string)))) contained within UrlHtmlFormatter? Why can't it be directly linked to "url+html"?

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  • Jquery post success variable scope

    - by minirobot
    Hi, I'm trying to return the ajax success array from one function to another. For some reason I don't seem to be able to pass the data stored in a variable in the success part of the ajax function into the parent function to return. Thanks so much for any assistance. Here's a simplified version of the code: // make json_to_return global var json_to_return; function loop_through_data(){ // call the load_days function and put its array data into days_array var days_data = load_days(03,2010); // I'd like to be able to iterate through days_data here // // } function load_days(selectedMonth, selectedYear){ $.ajax({ type: "POST", dataType: "json", url: "../includes/get_availability.php", data: "month=" + selectedMonth + "&year=" + selectedYear, success: function(available_json){ json_to_return = available_json; }, error: function(msg){ alert("error " + msg); } }); return json_to_return; }

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  • ruby on rails named scope implementation

    - by Engwan
    From the book Agile Web Development With Rails class Order < ActiveRecord::Base named_scope :last_n_days, lambda { |days| {:conditions => ['updated < ?' , days] } } named_scope :checks, :conditions => {:pay_type => :check} end The statement orders = Orders.checks.last_n_days(7) will result to only one query to the database. How does rails implement this? I'm new to Ruby and I'm wondering if there's a special construct that allows this to happen. To be able to chain methods like that, the functions generated by named_scope must be returning themselves or an object than can be scoped further. But how does Ruby know that it is the last function call and that it should query the database now? I ask this because the statement above actually queries the database and not just returns an SQL statement that results from chaining.

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  • Ruby IRB - Requires and Scope

    - by tyndall
    Trying to understand this problem I'm running into. I create file welcome.rb. The contents of this file: welcome_message = "hi there" I then launch an irb session. And type require 'welcome'. That works fine. Then I type: puts welcome_message I get the error message undefined local variable or method `welcome_message' for main:Object What is the best way to bring in predefined variables and have initialization work done when you require something into your irb session. Global variables didn't seem like the right path.

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  • Scope quandary with namespaces, function templates, and static data

    - by Adrian McCarthy
    This scoping problem seems like the type of C++ quandary that Scott Meyers would have addressed in one of his Effective C++ books. I have a function, Analyze, that does some analysis on a range of data. The function is called from a few places with different types of iterators, so I have made it a template (and thus implemented it in a header file). The function depends on a static table of data, AnalysisTable, that I don't want to expose to the rest of the code. My first approach was to make the table a static const inside Analysis. namespace MyNamespace { template <typename InputIterator> int Analyze(InputIterator begin, InputIterator end) { static const int AnalysisTable[] = { /* data */ }; ... // implementation uses AnalysisTable return result; } } // namespace MyNamespace It appears that the compiler creates a copy of AnalysisTable for each instantiation of Analyze, which is wasteful of space (and, to a small degree, time). So I moved the table outside the function like this: namespace MyNamespace { const int AnalysisTable[] = { /* data */ }; template <typename InputIterator> int Analyze(InputIterator begin, InputIterator end) { ... // implementation uses AnalysisTable return result; } } // namespace MyNamespace There's only one copy of the table now, but it's exposed to the rest of the code. I'd rather keep this implementation detail hidden, so I introduced an unnamed namespace: namespace MyNamespace { namespace { // unnamed to hide AnalysisTable const int AnalysisTable[] = { /* data */ }; } // unnamed namespace template <typename InputIterator> int Analyze(InputIterator begin, InputIterator end) { ... // implementation uses AnalysisTable return result; } } // namespace MyNamespace But now I again have multiple copies of the table, because each compilation unit that includes this header file gets its own. If Analyze weren't a template, I could move all the implementation detail out of the header file. But it is a template, so I seem stuck. My next attempt was to put the table in the implementation file and to make an extern declaration within Analyze. // foo.h ------ namespace MyNamespace { template <typename InputIterator> int Analyze(InputIterator begin, InputIterator end) { extern const int AnalysisTable[]; ... // implementation uses AnalysisTable return result; } } // namespace MyNamespace // foo.cpp ------ #include "foo.h" namespace MyNamespace { const int AnalysisTable[] = { /* data */ }; } This looks like it should work, and--indeed--the compiler is satisfied. The linker, however, complains, "unresolved external symbol AnalysisTable." Drat! (Can someone explain what I'm missing here?) The only thing I could think of was to give the inner namespace a name, declare the table in the header, and provide the actual data in an implementation file: // foo.h ----- namespace MyNamespace { namespace PrivateStuff { extern const int AnalysisTable[]; } // unnamed namespace template <typename InputIterator> int Analyze(InputIterator begin, InputIterator end) { ... // implementation uses PrivateStuff::AnalysisTable return result; } } // namespace MyNamespace // foo.cpp ----- #include "foo.h" namespace MyNamespace { namespace PrivateStuff { const int AnalysisTable[] = { /* data */ }; } } Once again, I have exactly one instance of AnalysisTable (yay!), but other parts of the program can access it (boo!). The inner namespace makes it a little clearer that they shouldn't, but it's still possible. Is it possible to have one instance of the table and to move the table beyond the reach of everything but Analyze?

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  • Variable Scope Problem, iPhone

    - by Stumf
    Hello all, I need some help here so I will do my best to explain. I have worked on this all day and had no success (just learning!) I have: NSArray *getValue(NSString *iosearch) { ................................. ................................... \\ More code here } - (NSString *) serialnumber { NSArray *results = getValue(@"serial-number"); if (results) return [results objectAtIndex:0]; return nil; } - (NSString *) backlightlevel { NSArray *results = getValue(@"backlight-level"); if (results) return [results objectAtIndex:0]; return nil; } I have a tableView set up and want to display my array in it so I then have: - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {............. ......................................................... cell.text = [results objectAtIndex:indexPath.row]; // error results undeclared here return cell; } The problem is I get results undeclared as indicated above. I also can't figure how I could get serialnumber and backlightlevel to display on the click of a button or even at load. My attempts have thrown back errors like error: 'serialnumber' undeclared (first use in this function) and warnings like warning: 'return' with a value, in function returning void. Sorry for the long question! Many thanks, Stuart

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  • Sinatra Variable Scope

    - by Ethan Turkeltaub
    Take the following code: ### Dependencies require 'rubygems' require 'sinatra' require 'datamapper' ### Configuration config = YAML::load(File.read('config.yml')) name = config['config']['name'] description = config['config']['description'] username = config['config']['username'] password = config['config']['password'] theme = config['config']['theme'] set :public, 'views/themes/#{theme}/static' ### Models DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/marvin.db") class Post include DataMapper::Resource property :id, Serial property :name, String property :body, Text property :created_at, DateTime property :slug, String end class Page include DataMapper::Resource property :id, Serial property :name, String property :body, Text property :slug, String end DataMapper.auto_migrate! ### Controllers get '/' do @posts = Post.get(:order => [ :id_desc ]) haml :"themes/#{theme}/index" end get '/:year/:month/:day/:slug' do year = params[:year] month = params[:month] day = params[:day] slug = params[:slug] haml :"themes/#{theme}/post.haml" end get '/:slug' do haml :"themes/#{theme}/page.haml" end get '/admin' do haml :"admin/index.haml" end I want to make name, and all those variables available to the entire script, as well as the views. I tried making them global variables, but no dice.

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  • anonymous function variable scope [js, ajax]

    - by arthurprs
    $(".delete").click( function() { var thesender = this; $(thesender).text("Del..."); $.getJSON("ajax.php", {}, function(data) { if (data["result"]) $(thesender).remove(); // variable defined outside else alert('Error!'); } ); return false; } ); This can cause problems if user clicks on another ".delete" before the ajax callback is called?

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  • How do i fix this JS scope in GM_xmlhttpRequest

    - by acidzombie24
    When i run this code alert 2 shows 6 different href links. alert 3 shows the last href 6 times. How do i make it use the same object (linkdom aka thelink) as alert 2. NOTE: This is in a greasemonkey script { var linkdom = thelink; alert('2' + linkdom.getAttribute("href")); GM_xmlhttpRequest({ method: 'GET', url: href, onload: function(resp){ //... alert('3' + linkdom.getAttribute("href")); } }); //... }

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  • Scope of object properties & methods

    - by Anish
    In the article Show love to the object literal, it's said: When we have several scripts in a page, the global variables & functions will get overwritten if their name repeats. One solution is to make the variables as properties & functions as methods of an object, and access them via the object name. But will this prevent the issue of variables getting into the global namespace? <script> var movie = { name: "a", trailer: function(){ //code } }; </script> In the above code which elements gets added to the global namespace? a) Just the object name - movie b) Object name as well as the properties and methods inside it – movie, movie.name, movie.trailer()

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  • javascript scope problem when lambda function refers to a variable in enclosing loop

    - by Stefan Blixt
    First question on stackoverflow :) Hope I won't embarrass myself... I have a javascript function that loads a list of albums and then it creates a list item for each album. The list item should be clickable, so I call jQuery's click() with a function that does stuff. I do this in a loop. My problem is that all items seem to get the same click function, even though I try to make a new one that does different stuff in each iteration. Another possibility is that the iteration variable is global somehow, and the function refers to it. Code below. debug() is just an encapsulation of Firebug's console.debug(). function processAlbumList(data, c) { for (var album in data) { var newAlbum = $('<li class="albumLoader">' + data[album].title + '</li>').clone(); var clickAlbum = function() { debug("contents: " + album); }; debug("Album: " + album + "/" + data[album].title); $('.albumlist').append(newAlbum); $(newAlbum).click(clickAlbum); } } Here is a transcript of what it prints when the above function runs, after that are some debug lines caused by me clicking on different items. It always prints "10", which is the last value that the album variable takes (there are 10 albums). Album: 0/Live on radio.electro-music.com Album: 1/Doodles Album: 2/Misc Stuff Album: 3/Drawer Collection Album: 4/Misc Electronic Stuff Album: 5/Odds & Ends Album: 6/Tumbler Album: 7/Bakelit 32 Album: 8/Film Album: 9/Bakelit Album: 10/Slow Zoom/Atomic Heart contents: 10 contents: 10 contents: 10 contents: 10 contents: 10 Any ideas? Driving me up the wall, this is. :) /Stefan

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  • jquery scope issue

    - by matthewb
    I am having issue with the following: I can't seem to keep the link I am selecting in each repeated item. The word "this" is getting lost. the Var event_id works for each element, but the var $something is undefined? Why is that, Ideally I wanted to do a switch statement but same issue, can't seem to get it to know what link I click and the elements around it to do the action. Updated Full Function: function rsvp (selector,function_url) { $(selector).livequery('click',function(){ var $select = $(selector).attr('rel'); var $event_id= $(this).parents('ul.event-options').attr('rel'); if ($select == "attending") { $(this).closest('span.rsvp-status').html("I'm Attending &ndash; <a href='javascript:;' class='remove' rel='remove'>Remove</a>"); var $something = $(this).parents('ul.event-options').attr('rel'); alert($something); } if ($select == "remove") { $(this).closest('span.rsvp-status').html("Not Attending &ndash; <a href='javascript:;' class='rsvp' rel='attending'>RSVP?</a>"); } if ($select == "interested") { $(this).closest('li').addClass('interested'); $(this).closest('li').removeClass('not-interested'); $(this).closest('li').html("You're Interested"); } $.ajax({ type: "POST", url: "/events/set_member/"+function_url, data: "event_id="+$event_id, beforeSend: function() { $("<span class='notice'>Updating...</span>").prependTo('body'); }, complete: function() { $('span.notice').fadeOut(500); } }); }); } rsvp ('a.rsvp','rsvp'); rsvp ('a.interests','interested'); rsvp ('a.remove','remove'); HTML <ul class="event-options" rel="<?=$event['event_id']?>"> <?php if($event['rsvp_total'] > 0) { ?> <!-- Show Only When Count is Greater than 0 --> <li class="group"><span class="total"><?= $event['rsvp_total']?></span>Interested </li> <?php } ?> <li class="rsvp"><span class="rsvp-status"> Not Attending &ndash; <a href="javascript:;" class="rsvp" rel="attending">RSVP?</a></span></li> <li class="not-interested"> <a href="javascript:;" class="interests" rel="interested"> Interested? </a> </li> <li class="place"><span><a href="<?=$place_path.$event['place_id']?>"><?=$event['place_name']?></a></span></li> <li class="share" rel="<?=$event['event_name']?>"> <a class="sharethis"></a> </li> </ul>

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  • Scope of "library" methods

    - by JS
    Hello, I'm apparently laboring under a poor understanding of Python scoping. Perhaps you can help. Background: I'm using the 'if name in "main"' construct to perform "self-tests" in my module(s). Each self test makes calls to the various public methods and prints their results for visual checking as I develop the modules. To keep things "purdy" and manageable, I've created a small method to simplify the testing of method calls: def pprint_vars(var_in): print("%s = '%s'" % (var_in, eval(var_in))) Calling pprint_vars with: pprint_vars('some_variable_name') prints: some_variable_name = 'foo' All fine and good. Problem statement: Not happy to just KISS, I had the brain-drizzle to move my handy-dandy 'pprint_vars' method into a separate file named 'debug_tools.py' and simply import 'debug_tools' whenever I wanted access to 'pprint_vars'. Here's where things fall apart. I would expect import debug_tools foo = bar debug_tools.pprint_vars('foo') to continue working its magic and print: foo = 'bar' Instead, it greets me with: NameError: name 'some_var' is not defined Irrational belief: I believed (apparently mistakenly) that import puts imported methods (more or less) "inline" with the code, and thus the variable scoping rules would remain similar to if the method were defined inline. Plea for help: Can someone please correct my (mis)understanding of scoping regards imports? Thanks, JS

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  • Rails Named Scope and overlapping conditions

    - by Tumtu
    Hi everyone, have a question about rails SQL generation: class Organization < ActiveRecord::Base has_many :people named_scope :active, :conditions => { :active => 'Yes' } end class Person < ActiveRecord::Base belongs_to :organization end Rails SQL for all active people in the first organiztion Organization.first.people.active.all [4;36;1mOrganization Load (0.0ms)[0m [0;1mSELECT TOP 1 * FROM [organizations] [0m [4;35;1mPerson Load (0.0ms)[0m [0mSELECT * FROM [people] WHERE ((([people].[active] = 'Yes') AND ([people].organization_id = 1)) AND ([people].organization_id = 1)) [0m Why Rails generates "[people].organization_id = 1" condition twice ? Does someone know how to make it DRY ? e.g. SELECT * FROM [people] WHERE (([people].[active] = 'Yes') AND ([people].organization_id = 1))

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  • PHP scope question

    - by Dan
    Hi, I'm trying to look through an array of records (staff members), in this loop, I call a function which returns another array of records (appointments for each staff member). foreach($staffmembers as $staffmember) { $staffmember['appointments'] = get_staffmember_appointments_for_day($staffmember); // print_r($staffmember['appointments'] works fine } This is working OK, however, later on in the script, I need to loop through the records again, this time making use of the appointment arrays, however they are unavailable. foreach ($staffmembers as $staffmember) { //do some other stuff //print_r($staffmember['appointments'] no longer does anything } Normally, I would perform the function from the first loop, within the second, however this loop is already nested within two others, which would cause the same sql query to be run 168 times. Can anyone suggest a workaround? Any advice would be greatly appreciated. Thanks

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  • Property Scope (Iphone)

    - by Hank
    Hello All. I am having trouble accessing a declared property and I think I am missing something fundamental about the nature of properties and perhaps view controllers. Here's what I'm doing so far: declaring a property "myPhone" in a root view controller called RootViewController. grabbing a phone number from a modally presented people picker setting "myPhone" to the value from the people picker (from within shouldContinueAfterSelectingPerson of ABPeoplePickerNavigationController) trying to access "myPhone" from another modally presented view controller "myPhone" continues to NSLog to null despite trying every permutation of self.myPhone, super, RootViewController, etc. to try and access the value I set. What am I missing?

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  • C pointer array scope and function calls

    - by juvenis
    I have this situation: { float foo[10]; for (int i = 0; i < 10; i++) { foo[i] = 1.0f; } object.function1(foo); // stores the float pointer to a const void* member of object } object.function2(); // uses the stored void pointer Are the contents of the float pointer unknown in the second function call? It seems that I get weird results when I run my program. But if I declare the float foo[10] to be const and initialize it in the declaration, I get correct results. Why is this happening?

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  • jQuery variables and scope

    - by Peuge
    I am writing a jQuery plugin and am running into a few problems with regard to variables. For example I have the following skeleton structure for my plugin, which is going to act on a textbox. In my init function I want to set a variable and bind a keypress event to my textbox. That keypress event needs to call another function, in which I need the variable. Is this possible? (function($){ var methods = { init : function(options){ return this.each(function(){ var $this = $(this); var someVar = 'somevar'; $this.keypress(function(event){ //I want to call my customFunction }); }); }, customFunction : function(){ //I am wanting to access 'someVar' here }; $.fn.mynamespace = function(method){ //handle which method to call here }; })(jQuery); Many thanks in advance.

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  • Javascript: Access the right scope "under" apply(...)

    - by Chau
    This is a very old problem, but I cannot seem to get my head around the other solutions presented here. I have an object function ObjA() { var a = 1; this.methodA = function() { alert(a); } } which is instantiated like var myObjA = new ObjA(); Later on, I assign my methodA as a handler function in an external Javascript Framework, which invokes it using the apply(...) method. When the external framework executes my methodA, this belongs to the framework function invoking my method. Since I cannot change how my method is called, how do I regain access to the private variable a? My research tells me, that closures might be what I'm looking for.

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