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• How is this algorithm, for finding maximum path on a Directed Acyclical Graph, called?

  - by Martín Fixman

  Since some time, I'm using an algorithm that runs in complexity O(V + E) for finding maximum path on a Directed Acyclical Graph from point A to point B, that consists on doing a flood fill to find what nodes are accessible from note A, and how many "parents" (edges that come from other nodes) each node has. Then, I do a BFS but only "activating" a node when I already had used all its "parents". queue <int> a int paths[] ; //Number of paths that go to note i int edge[][] ; //Edges of a int mpath[] ; //max path from 0 to i (without counting the weight of i) int weight[] ; //weight of each node mpath[0] = 0 a.push(0) while not empty(a) for i in edge[a] paths[i] += 1 a.push(i) while not empty(a) for i in children[a] mpath[i] = max(mpath[i], mpath[a] + weight[a]) ; paths[i] -= 1 ; if path[i] = 0 a.push(i) ; Is there any special name for this algorithm? I told it to an Informatics professor, he just called it "Maximum Path on a DAG", but it doesn't sound good when you say "I solved the first problem with a Fenwick Tree, the second with Dijkstra, and the third with Maximum Path".

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• C++ interpreter conceptual problem

  - by Jan Wilkins

  I've built an interpreter in C++ for a language created by me. One main problem in the design was that I had two different types in the language: number and string. So I have to pass around a struct like: class myInterpreterValue { myInterpreterType type; int intValue; string strValue; } Objects of this class are passed around million times a second during e.g.: a countdown loop in my language. Profiling pointed out: 85% of the performance is eaten by the allocation function of the string template. This is pretty clear to me: My interpreter has bad design and doesn't use pointers enough. Yet, I don't have an option: I can't use pointers in most cases as I just have to make copies. How to do something against this? Is a class like this a better idea? vector<string> strTable; vector<int> intTable; class myInterpreterValue { myInterpreterType type; int locationInTable; } So the class only knows what type it represents and the position in the table This however again has disadvantages: I'd have to add temporary values to the string/int vector table and then remove them again, this would eat a lot of performance again. Help, how do interpreters of languages like Python or Ruby do that? They somehow need a struct that represents a value in the language like something that can either be int or string.

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• How do I remove HTML that I place dynamically with JQuery

  - by Vivek

  lets say i have fallowing html... <li><a href="#" id='DataSheets' >Data Sheets</a><font class="leftNavHitsFont">- (1)</font></li> <li><a href="#" id='ApplicationNotes' >Application Notes</a><fontclass="leftNavHitsFont">- (6)</font></li> what i want to do is, add a html on onclick of these links, if you click on first link output should look like <li><span>ajksdfskaj</span></li> <li><a href="#" id='ApplicationNotes' >Application Notes</a><fontclass="leftNavHitsFont">- (6)</font></li> means hide the original html of that li and append new html for ex. a span as i have written above...and if i clicked on second link the first li should get it's original html and appended html should get removed and get appended to current li bieng clicked..in this case output should look like... <li><a href="#" id='DataSheets' >Data Sheets</a><font class="leftNavHitsFont">- (1)</font></li> <li><span>ajksdfskaj</span></li> i tried to achieve this thing through variuos way...but could not find out the correct way.. please help me out guys.. Thanks in advance!!!!

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• Why is my django bulk database population so slow and frequently failing?

  - by bryn

  I decided I'd like to use django's model system rather than coding raw SQL to interface with my database, but I am having a problem that surely is avoidable. My models.py contains: class Student(models.Model): student_id = models.IntegerField(unique = True) form = models.CharField(max_length = 10) preferred = models.CharField(max_length = 70) surname = models.CharField(max_length = 70) and I'm populating it by looping through a list as follows: from models import Student for id, frm, pref, sname in large_list_of_data: s = Student(student_id = id, form = frm, preferred = pref, surname = sname) s.save() I don't really want to be saving this to the database each time but I don't know another way to get django to not forget about it (I'd rather add all the rows and then do a single commit). There are two problems with the code as it stands. It's slow -- about 20 students get updated each second. It doesn't even make it through large_list_of_data, instead throwing a DatabaseError saying "unable to open database file". (Possibly because I'm using sqlite3.) My question is: How can I stop these two things from happening? I'm guessing that the root of both problems is that I've got the s.save() but I don't see a way of easily batching the students up and then saving them in one commit to the database.

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• How to repeatedly show a Dialog with PyGTK / Gtkbuilder?

  - by Julian

  I have created a PyGTK application that shows a Dialog when the user presses a button. The dialog is loaded in my __init__ method with: builder = gtk.Builder() builder.add_from_file("filename") builder.connect_signals(self) self.myDialog = builder.get_object("dialog_name") In the event handler, the dialog is shown with the command self.myDialog.run(), but this only works once, because after run() the dialog is automatically destroyed. If I click the button a second time, the application crashes. I read that there is a way to use show() instead of run() where the dialog is not destroyed, but I feel like this is not the right way for me because I would like the dialog to behave modally and to return control to the code only after the user has closed it. Is there a simple way to repeatedly show a dialog using the run() method using gtkbuilder? I tried reloading the whole dialog using the gtkbuilder, but that did not really seem to work, the dialog was missing all child elements (and I would prefer to have to use the builder only once, at the beginning of the program). [SOLUTION] As pointed out by the answer below, using hide() does the trick. But one has to take care that the dialog is in fact destroyed if one does not catch its "delete-event". A simple example that works is: import pygtk import gtk class DialogTest: def rundialog(self, widget, data=None): self.dia.show_all() result = self.dia.run() def destroy(self, widget, data=None): gtk.main_quit() def closedialog(self, widget, data=None): self.dia.hide() return True def __init__(self): self.window = gtk.Window(gtk.WINDOW_TOPLEVEL) self.window.connect("destroy", self.destroy) self.dia = gtk.Dialog('TEST DIALOG', self.window, gtk.DIALOG_MODAL | gtk.DIALOG_DESTROY_WITH_PARENT) self.dia.vbox.pack_start(gtk.Label('This is just a Test')) self.dia.connect("delete-event", self.closedialog) self.button = gtk.Button("Run Dialog") self.button.connect("clicked", self.rundialog, None) self.window.add(self.button) self.button.show() self.window.show() if __name__ == "__main__": testApp = DialogTest() gtk.main()

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• Calling button in Action Script 3.0

  - by Meko

  I am trying to make button panel. each button have two type btn_home and btn_home_white I am trying to reach those buttons.It is work if I write for each button their own methods like btn_home.addEventListener(MouseEvent.MOUSE_OVER,overEffect); btn_home_white.addEventListener(MouseEvent.MOUSE_OUT,outEffect); function overEffect(e:MouseEvent) { var myTweenHight:Tween = new Tween( btn_home,"height",Bounce.easeOut,25,0,3,true); var myTweenHight2:Tween = new Tween(btn_home_white,"height",Bounce.easeOut,0,25,3,true); var myTweenAlpha:Tween = new Tween(btn_home_white,"alpha",Strong.easeOut,0,1,2,true); } function outEffect(e:MouseEvent) { var myTweenHight:Tween = new Tween btn_home,"height",Bounce.easeOut,0,25,3,true); var myTweenHight2:Tween = new Tween(btn_home_white,"height",Bounce.easeOut,25,0,3,true); var myTweenAlpha:Tween = new Tween(btn_home_white,"alpha",Strong.easeOut,1,0,2,true); } But I have 10 buttons as btn_buttonname and btn_buttonname_white . I tryed to create Event listener on stage for all.It works for firts type buttons btn_buttonname but How can I get second type buttons? I tryed e.target["_white"] but it does not work . stage.addEventListener(MouseEvent.MOUSE_OVER , overEffect); stage.addEventListener(MouseEvent.MOUSE_OUT , outEffect); function overEffect(e:MouseEvent) { var myTweenHight:Tween = new Tween(e.target,"height",Bounce.easeOut,25,0,3,true); trace("height"); var myTweenHight2:Tween = new Tween(e.target["_white"],"height",Bounce.easeOut,0,25,3,true); var myTweenAlpha:Tween = new Tween(e.target["_white"],"alpha",Strong.easeOut,0,1,2,true); } function outEffect(e:MouseEvent) { var myTweenHight:Tween = new Tween(e.target,"height",Bounce.easeOut,0,25,3,true); var myTweenHight2:Tween = new Tween(e.target["_white"],"height",Bounce.easeOut,25,0,3,true); var myTweenAlpha:Tween = new Tween(e.target["_white"],"alpha",Strong.easeOut,1,0,2,true); }

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• Implementation/interface inheritance design question.

  - by Neil G

  I would like to get the stackoverflow community's opinion on the following three design patterns. The first is implementation inheritance; the second is interface inheritance; the third is a middle ground. My specific question is: Which is best? implementation inheritance: class Base { X x() const = 0; void UpdateX(A a) { y_ = g(a); } Y y_; } class Derived: Base { X x() const { return f(y_); } } interface inheritance: class Base { X x() const = 0; void UpdateX(A a) = 0; } class Derived: Base { X x() const { return x_; } void UpdateX(A a) { x_ = f(g(a)); } X x_; } middle ground: class Base { X x() const { return x_; } void UpdateX(A a) = 0; X x_; } class Derived: Base { void UpdateX(A a) { x_ = f(g(a)); } } I know that many people prefer interface inheritance to implementation inheritance. However, the advantage of the latter is that with a pointer to Base, x() can be inlined and the address of x_ can be statically calculated.

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• Getting unpredictable data into a tabular format

  - by Acorn

  The situation: Each page I scrape has <input> elements with a title= and a value= I don't know what is going to be on the page. I want to have all my collected data in a single table at the end, with a column for each title. So basically, I need each row of data to line up with all the others, and if a row doesn't have a certain element, then it should be blank (but there must be something there to keep the alignment). eg. First page has: {animal: cat, colour: blue, fruit: lemon, day: monday} Second page has: {animal: fish, colour: green, day: saturday} Third page has: {animal: dog, number: 10, colour: yellow, fruit: mango, day: tuesday} Then my resulting table should be: animal | number | colour | fruit | day cat | none | blue | lemon | monday fish | none | green | none | saturday dog | 10 | yellow | mango | tuesday Although it would be good to keep the order of the title value pairs, which I know dictionaries wont do. So basically, I need to generate columns from all the titles (kept in order but somehow merged together) What would be the best way of going about this without knowing all the possible titles and explicitly specifying an order for the values to be put in?

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• Broken console in Maven project using Netbeans

  - by Maciek Sawicki

  Hi, I have strange problem with my Neatens+Maven installation. This is the shortest code to reproduce the problem: public class App { public static void main( String[] args ) { // Create a scanner to read from keyboard Scanner scanner = new Scanner (System.in); Scanner s= new Scanner(System.in); String param= s.next(); System.out.println(param); } } When I'm running it as Maven Project inside Netbeans console seems to be broken. It just ignores my input. It's look like infinitive loop in System.out.println(param);. However this project works fine when it's compiled as "Java Aplication" project. It also works O.K. if I build and run it from cmd. System info: Os: Vista IDE: Netbeans 6.8 Maven: apache-maven-2.2.1 //edit Built program (using mavean from Netbeans) works fine. I just can't test it using Net beans. And I think I forgot to ask the question ;). So of course my first question is: how can I fix this problem? And second is: Is it any workaround for this? For example configuring Netbeans to run external commend line app instead of using built in console.

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• Pairs from single list

  - by Apalala

  Often enough, I've found the need to process a list by pairs. I was wondering which would be the pythonic and efficient way to do it, and found this on Google: pairs = zip(t[::2], t[1::2]) I thought that was pythonic enough, but after a recent discussion involving idioms versus efficiency, I decided to do some tests: import time from itertools import islice, izip def pairs_1(t): return zip(t[::2], t[1::2]) def pairs_2(t): return izip(t[::2], t[1::2]) def pairs_3(t): return izip(islice(t,None,None,2), islice(t,1,None,2)) A = range(10000) B = xrange(len(A)) def pairs_4(t): # ignore value of t! t = B return izip(islice(t,None,None,2), islice(t,1,None,2)) for f in pairs_1, pairs_2, pairs_3, pairs_4: # time the pairing s = time.time() for i in range(1000): p = f(A) t1 = time.time() - s # time using the pairs s = time.time() for i in range(1000): p = f(A) for a, b in p: pass t2 = time.time() - s print t1, t2, t2-t1 These were the results on my computer: 1.48668909073 2.63187503815 1.14518594742 0.105381965637 1.35109519958 1.24571323395 0.00257992744446 1.46182489395 1.45924496651 0.00251388549805 1.70076990128 1.69825601578 If I'm interpreting them correctly, that should mean that the implementation of lists, list indexing, and list slicing in Python is very efficient. It's a result both comforting and unexpected. Is there another, "better" way of traversing a list in pairs? Note that if the list has an odd number of elements then the last one will not be in any of the pairs. Which would be the right way to ensure that all elements are included? I added these two suggestions from the answers to the tests: def pairwise(t): it = iter(t) return izip(it, it) def chunkwise(t, size=2): it = iter(t) return izip(*[it]*size) These are the results: 0.00159502029419 1.25745987892 1.25586485863 0.00222492218018 1.23795199394 1.23572707176 Results so far Most pythonic and very efficient: pairs = izip(t[::2], t[1::2]) Most efficient and very pythonic: pairs = izip(*[iter(t)]*2) It took me a moment to grok that the first answer uses two iterators while the second uses a single one. To deal with sequences with an odd number of elements, the suggestion has been to augment the original sequence adding one element (None) that gets paired with the previous last element, something that can be achieved with itertools.izip_longest().

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• jQuery rotator not rotating properly - too much recursion

  - by Matt Nathanson

  I've built a custom jQuery rotator using just basic animation to rotate the 3 Divs (images). I've built the function and then reinitiate the function using it as a call back. Here's the code: function ImageRotate() { var CurrentFeature = "#container" + featureNumber; $(CurrentFeature).stop(false, true).delay(4500).animate({'top' : '330px'}, 3000); var featureNumber2 = featureNumber-1; if ( featureNumber == 1) {featureNumber2=3} var CurrentFeature2 = "#container" + featureNumber2; $(CurrentFeature2).stop(false, true).delay(4500).animate({'top' : '0px'}, 3000); $('#container2').stop(false, true).delay(4500).animate({'top' : '-330px'}, 25); var featureNumber3 = featureNumber+1; if ( featureNumber == 3){featureNumber3=1} var CurrentFeature3 = "#container" + featureNumber3; $(CurrentFeature3).stop(false, true).delay(7500).animate({'top' : '0px'}, 3000); $(CurrentFeature2).stop(false, true).delay(4500).animate({'top' : '330px'}, 3000); $(CurrentFeature).stop(false, true).delay(4500).animate({'top' : '-330px'}, 25); if (featureNumber ==1) {featureNumber=3} else{featureNumber--}; $(CurrentFeature).stop(false, true).delay(7500).animate({'top' : '0px'}, 3000); $(CurrentFeature3).stop(false, true).delay(4500).animate({'top' : '330px'}, 3000); $(CurrentFeature2).stop(false, false).delay(4500).animate({'top' : '-330px'}, 25,ImageRotate()); }; It's worth noting that when calling the function again I also tried making another function called ImageRotate2(); and it did the same thing. It loops, but i get all sorts of funkiness. Edit: I've also tried some answers in the replies and they both leave me with recursion errors each second.

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• Syntactical analysis with Flex/Bison part 2

  - by Imran

  Hallo, I need help in Lex/Yacc Programming. I wrote a compiler for a syntactical analysis for inputs of many statements. Now i have a special problem. In case of an Input the compiler gives the right output, which statement is uses, constant operator or a jmp instructor to which label, now i have to write so, if now a if statement comes, first the first command (before the else) must be give out when the assignment of the if is yes then it must jump to the end because the command after the else isnt needed, so after this jmp then the second command must be give out. I show it in an example maybe you understand what i mean. Input adr. Output if(x==0) 10 if(x==0) Wait 5 20 WAIT 5 else 30 JMP 50 Wait 1 40 WAIT 1 end 50 END like so. I have an idea, maybe i can do it whith a special if statement like IF exp jmp_stmt_end stmt_seq END when the if statement is given in the input the compiler has to recognize the end ofthe statement and like my jmp_stmt in my compiler ( you have to download the files from http://bitbucket.org/matrix/changed-tiny) only to jump to the end. I hope you understand my problem.thanks.

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• Python - Checking for membership inside nested dict

  - by victorhooi

  heya, This is a followup questions to this one: http://stackoverflow.com/questions/2901422/python-dictreader-skipping-rows-with-missing-columns Turns out I was being silly, and using the wrong ID field. I'm using Python 3.x here. I have a dict of employees, indexed by a string, "directory_id". Each value is a nested dict with employee attributes (phone number, surname etc.). One of these values is a secondary ID, say "internal_id", and another is their manager, call it "manager_internal_id". The "internal_id" field is non-mandatory, and not every employee has one. (I've simplified the fields a little, both to make it easier to read, and also for privacy/compliance reasons). The issue here is that we index (key) each employee by their directory_id, but when we lookup their manager, we need to find managers by their "internal_id". Before, when employee.keys() was a list of internal_ids, I was using a membership check on this. Now, the last part of my if statement won't work, since the internal_ids is part of the dict values, instead of the key itself. def lookup_supervisor(manager_internal_id, employees): if manager_internal_idis not None and manager_internal_id!= "" and manager_internal_id in employees.keys(): return (employees[manager_internal_id]['mail'], employees[manager_internal_id]['givenName'], employees[manager_internal_id]['sn']) else: return ('Supervisor Not Found', 'Supervisor Not Found', 'Supervisor Not Found') So the first question is, how do I check whether the manager_internal_id is present in the dict's values. I've tried substituting employee.keys() with employee.values(), that didn't work. Also, I'm hoping for something a little more efficient, not sure if there's a way to get a subset of the values, specifically, all the entries for employees[directory_id]['internal_id']. Hopefully there's some Pythonic way of doing this, without using a massive heap of nested for/if loops. My second question is, how do I then cleanly return the required employee attributes (mail, givenname, surname etc.). My for loop is iterating over each employee, and calling lookup_supervisor. I'm feeling a bit stupid/stumped here. def tidy_data(employees): for directory_id, data in employees.items(): # We really shouldnt' be passing employees back and forth like this - hmm, classes? data['SupervisorEmail'], data['SupervisorFirstName'], data['SupervisorSurname'] = lookup_supervisor(data['manager_internal_id'], employees) Thanks in advance =), Victor

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• Looping and pausing after loading ajax content in Javascript JQuery

  - by Tristan

  I have what I though was a simple problem to solve (never is!) I'm trying to loop through a list of URL's in a javascript array I have made, load the first one, wait X seconds, then load the second, and continue until I start again. I got the array and looping working, trouble is, however I try and implement a "wait" using setInterval or similar, I have a structural issue, as the loop continues in the background. I tried to code it like this: $(document).ready(function(){ // my array of URL's var urlArray = new Array(); urlArray[0] = "urlOne"; urlArray[1] = "urlTwo"; urlArray[2] = "urlThree"; // my looping logic that continues to execute (problem starts here) while (true) { for (var i = 0; i < urlArray.length; i++) { $('#load').load(urlArray[i], function(){ // now ideally I want it to wait here for X seconds after loading that URL and then start the loop again, but javascript doesn't seem to work this way, and I'm not sure how to structure it to get the same effect }); } } });

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• Synchronizing DataGridView (DataTable) with the DB

  - by Ezekiel Rage

  Hi! I have the following situation: there is a table in the DB that is queried when the form loads and the retrieved data is filled into a DataGridView via the DataTable underneath. After the data is loaded the user is free to modify the data (add / delete rows, modify entries). The form has 2 buttons: Apply and Refresh. The first one sends the changes to the database, the second one re-reads the data from the DB and erases any changes that have been made by the user. My question is: is this the best way to keep a DataGridView synchronized with the DB (from a users point of view)? For now these are the downsides: the user must keep track of what he is doing and must press the button every while the modifications are lost if the form is closed / app crash / ... I tried sending the changes to the DB on CellEndEdit event but then the user also needs some Undo/Redo functionality and that is ... well ... a different story. So, any suggestions?

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• How to implement a Client-side Ajax Login on Asp.Net MVC (A link to the solution for Asp.Net Webform

  - by Matt

  Hi, I'm trying to implement a client-side ajax login on Asp.Net MVC. I used to have this set up just fine on WebForms, but now that I've moved to MVC it's giving me some troubles. If you'd like a tutorial on Client-side Ajax Login for Asp.Net Webforms, it can be found here -- Easy, A++ Now... for some reason it's not working for Asp.Net MVC. I used the exact same tutorial as for the Webforms, except when it executes the ssa.login() (equivalently: Sys.Services.AuthenticationService.login()) it's not doing anything. I have alerts in both the onLoginComplete() function and the onError() function. As well I have an alert before the ssa.login gets called and right after... function loginHandler() { var username = $("#login_UserName").val(); var password = $("#login_Password").val(); var isPersistent = $("#login_RememberMe").attr("checked"); var customInfo = null; var redirectUrl = null; // Log them in. alert("try login"); ssa.login(username, password, isPersistent, customInfo, redirectUrl, onLoginComplete, onError); alert("made it here"); } The first alert fires but the second one doesn't which means the function is failing. Here's the function I pulled from Asp.Net Ajax to show you: function(c, b, a, h, f, d, e, g) { this._invoke(this._get_path(), "Login", false, { userName: c, password: b, createPersistentCookie: a }, Function.createDelegate(this, this._onLoginComplete), Function.createDelegate(this, this._onLoginFailed), [c, b, a, h, f, d, e, g]); } Anyone have any idea of why it's failing?

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• Can I specify default value?

  - by atch

  Why is it that for user defined types when creating an array of objects every element of this array is initialized with default ctor but when I create built-in type this isn't the case? And second question: is it possible to specify default value to be used while initialize? Something like this (not valid): char* p = new char[size]('\0'); And another question in this topic while I'm with arrays. I suppose that when creating an array of user defined type and knowing the fact that every elem. of this array will be initialized with default value firstly why? If arrays for built in types do not initialize their elems. with their dflts why do they do it for UDT, and secondly: is there a way to switch it off/avoid/circumvent somehow? It seems like bit of a waste if I for example have created an array with size 10000 and then 10000 times dflt ctor will be invoked and I will (later on) overwrite this values anyway. I think that behaviour should be consistent, so either every type of array should be initialized or none. And I think that the behaviour for built-in arrays is more appropriate.

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• Unit Testing-- fundamental goal?

  - by David

  Me and my co-workers had a bit of a disagreement last night about unit testing in our PHP/MySQL application. Half of us argued that when unit testing a function within a class, you should mock everything outside of that class and its parents. The other half of us argued that you SHOULDN'T mock anything that is a direct dependancy of the class either. The specific example was our logging mechanism, which happened through a static Logging class, and we had a number of Logging::log() calls in various locations throughout our application. The first half of us said the Logging mechanism should be faked (mocked) because it would be tested in the Logging unit tests. The second half of us argued that we should include the original Logging class in our unit test so that if we make a change to our logging interface, we'll be able to see if it creates problems in other parts of the application due to failing to update the call interface. So I guess the fundamental question is-- do unit tests serve to test the functionality of a single unit in a closed environment, or show the consequences of changes to a single unit in a larger environment? If it's one of these, how do you accomplish the other?

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• Macro to improve callback registration readability

  - by Warren Seine

  I'm trying to write a macro to make a specific usage of callbacks in C++ easier. All my callbacks are member functions and will take this as first argument and a second one whose type inherits from a common base class. The usual way to go is: register_callback(boost::bind(&my_class::member_function, this, _1)); I'd love to write: register_callback(HANDLER(member_function)); Note that it will always be used within the same class. Even if typeof is considered as a bad practice, it sounds like a pretty solution to the lack of __class__ macro to get the current class name. The following code works: typedef typeof(*this) CLASS; boost::bind(& CLASS :: member_function, this, _1)(my_argument); but I can't use this code in a macro which will be given as argument to register_callback. I've tried: #define HANDLER(FUN) \ boost::bind(& typeof(*this) :: member_function, this, _1); which doesn't work for reasons I don't understand. Quoting GCC documentation: A typeof-construct can be used anywhere a typedef name could be used. My compiler is GCC 4.4, and even if I'd prefer something standard, GCC-specific solutions are accepted.

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• How to create an instance of object with RTTI in Delphi 2010?

  - by Paul

  As we all known, when we call a constructor of a class like this: instance := TSomeClass.Create; The Delphi compiler actually do the following things: Call the static NewInstance method to allocate memory and initialize the memory layout. Call the constructor method to perform the initialization of the class Call the AfterConstruction method It's simple and easy to understand. but I'm not very sure how the compiler handle exceptions in the second and the third step. It seems there are no explicit way to create an instance using a RTTI constructor method in D2010. so I wrote a simple function in the Spring Framework for Delphi to reproduce the process of the creation. class function TActivator.CreateInstance(instanceType: TRttiInstanceType; constructorMethod: TRttiMethod; const arguments: array of TValue): TObject; var classType: TClass; begin TArgument.CheckNotNull(instanceType, 'instanceType'); TArgument.CheckNotNull(constructorMethod, 'constructorMethod'); classType := instanceType.MetaclassType; Result := classType.NewInstance; try constructorMethod.Invoke(Result, arguments); except on Exception do begin if Result is TInterfacedObject then begin Dec(TInterfacedObjectHack(Result).FRefCount); end; Result.Free; raise; end; end; try Result.AfterConstruction; except on Exception do begin Result.Free; raise; end; end; end; I feel it maybe not 100% right. so please show me the way. Thanks!

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• How to define trees with more than one type in ML programing language

  - by user550413

  Well, I am asked to do the next thing: To define a binary tree which can contain 2 different types: ('a,'b) abtree and these are the requirements: Any inner vertex (not a leaf) must be of the type 'a or 'b and the leafs have no value. For every path in the tree all 'a values must appear before the 'b value: examples of paths: 'a->'a->'a-'b (legal) 'a->'b->'b (legal) 'a->'a->'a (legal) 'b->'b->'b (legal) 'a->'b->'a (ILLEGAL) and also I need to define another tree which is like the one described above but now I have got also 'c and in the second requirement it says that for every path I 'a values appear before the 'b values and all the 'b values appear before the 'c values. First, I am not sure how to define binary trees to have more than 1 type in them. I mean the simplest binary tree is: datatype 'a tree = leaf | br of 'a * 'a tree * 'a tree; And also how I can define a tree to have these requirements. Any help will be appreciated. Thanks.

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• SQL: select rows with the same order as IN clause

  - by Andrea3000

  I know that this question has been asked several times and I've read all the answer but none of them seem to completely solve my problem. I'm switching from a mySQL database to a MS Access database with MS SQL. In both of the case I use a php script to connect to the database and perform SQL queries. I need to find a suitable replacement for a query I used to perform on mySQL. I want to: perform a first query and order records alphabetically based on one of the columns construct a list of IDs which reflects the previous alphabetical order perform a second query with the IN clause applied with the IDs' list and ordered by this list. In mySQL I used to perform the last query this way: SELECT name FROM users WHERE id IN ($name_ids) ORDER BY FIND_IN_SET(id,'$name_ids') Since FIND_IN_SET is available only in mySQL and CHARINDEX and PATINDEX are not available from my php script, how can I achieve this? I know that I could write something like: SELECT name FROM users WHERE id IN ($name_ids) ORDER BY CASE id WHEN ... THEN 1 WHEN ... THEN 2 WHEN ... THEN 3 WHEN ... THEN 4 END but you have to consider that: IDs' list has variable length and elements because it depends on the first query that list can easily contains thousands of elements Have you got any hint on this? Is there a way to programmatically construct the ORDER BY CASE ... WHEN ... statement? Is there a better approach since my list of IDs can be big?

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• User defined literal arguments are not constexpr?

  - by Pubby

  I'm testing out user defined literals. I want to make _fac return the factorial of the number. Having it call a constexpr function works, however it doesn't let me do it with templates as the compiler complains that the arguments are not and cannot be constexpr. I'm confused by this - aren't literals constant expressions? The 5 in 5_fac is always a literal that can be evaluated during compile time, so why can't I use it as such? First method: constexpr int factorial_function(int x) { return (x > 0) ? x * factorial_function(x - 1) : 1; } constexpr int operator "" _fac(unsigned long long x) { return factorial_function(x); // this works } Second method: template <int N> struct factorial { static const unsigned int value = N * factorial<N - 1>::value; }; template <> struct factorial<0> { static const unsigned int value = 1; }; constexpr int operator "" _fac(unsigned long long x) { return factorial_template<x>::value; // doesn't work - x is not a constexpr }

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• In App Purchase Unique Identifying Data

  - by dageshi

  O.K so I'm writing a iPhone travel guide, you purchase a subscription to a travel guide for 3 months, it downloads a fairly hefty database and for 3 months that database gets updated weekly with new stuff. Now what I'd like to do is make the user enter their email address as a one off action before they purchase their first guide, for China say. The purpose for doing this is 1) To allow me to contact the user by email when they add a note/tip for a particular place (the app will allow them to send notes & information to me) 2) To Uniquely identify who has purchased the subscription so that if they wipe their device and reinstall the app they can plug the email address in and pickup their subscriptions again. Or so they can use the same subscription on another device they own. My concerns are 1) Will Apple allow the email method of restoring functionality to a second or restored device? 2) As long as I tell the user what I'm using their email address for (aka I won't sell it to anyone else and use it for X purposes) will it be o.k to ask for said email address? And as a side note, can I tack the devices unique id onto my server comms to track devices or is apple going to through a hissy fit about that as well?

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• XmlDocument.Load() throws XmlSchemaValidationException

  - by Praetorian

  Hi, I'm trying to validate an XML document against a schema (which is embedded in my program as a resource). I got everything to work, so I tried to test for errors by adding a second sibling node in the XML at a location where the schema specifies maxOccurs="1". The problem is that my ValidationEventHandler is never getting called, also XmlDocument.Load() is throwing an XmlSchemaValidationException exception when I'd expected XmlDocument.Validate() to do that. This is the code I have: private void ValidateUserData( string xmlPath ) { var resInfo = Application.GetResourceStream( new Uri( @"MySchema.xsd", UriKind.Relative ) ); var schema = XmlSchema.Read( resInfo.Stream, SchemaValidationCallBack ); XmlSchemaSet schemaSet = new XmlSchemaSet(); schemaSet.Add( schema ); schemaSet.ValidationEventHandler += SchemaValidationCallBack; XmlReaderSettings settings = new XmlReaderSettings(); settings.Schemas = schemaSet; settings.ValidationType = ValidationType.Schema; XmlDocument doc = new XmlDocument(); using( XmlReader reader = XmlReader.Create( xmlPath, settings ) ) { doc.Load( reader ); // <-- This line throws an exception if XML is ill-formed reader.Close(); } doc.Validate( SchemaValidationCallBack );// <-- This is never reached } private void SchemaValidationCallBack( object sender, ValidationEventArgs e ) { Console.WriteLine( "SchemaValidationCallBack: " + e.Message ); } How do I get the callback to be called so I can handle validation errors? Thanks for your help!

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