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  • C# Nested Property Accessing overloading OR Sequential Operator Overloading

    - by Tim
    Hey, I've been searching around for a solution to a tricky problem we're having with our code base. To start, our code resembles the following: class User { int id; int accountId; Account account { get { return Account.Get(accountId); } } } class Account { int accountId; OnlinePresence Presence { get { return OnlinePresence.Get(accountId); } } public static Account Get(int accountId) { // hits a database and gets back our object. } } class OnlinePresence { int accountId; bool isOnline; public static OnlinePresence Get(int accountId) { // hits a database and gets back our object. } } What we're often doing in our code is trying to access the account Presence of a user by doing var presence = user.Account.Presence; The problem with this is that this is actually making two requests to the database. One to get the Account object, and then one to get the Presence object. We could easily knock this down to one request if we did the following : var presence = UserPresence.Get(user.id); This works, but sort of requires developers to have an understanding of the UserPresence class/methods that would be nice to eliminate. I've thought of a couple of cool ways to be able to handle this problem, and was wondering if anyone knows if these are possible, if there are other ways of handling this, or if we just need to think more as we're coding and do the UserPresence.Get instead of using properties. Overload nested accessors. It would be cool if inside the User class I could write some sort of "extension" that would say "any time a User object's Account property's Presence object is being accessed, do this instead". Overload the . operator with knowledge of what comes after. If I could somehow overload the . operator only in situations where the object on the right is also being "dotted" it would be great. Both of these seem like things that could be handled at compile time, but perhaps I'm missing something (would reflection make this difficult?). Am I looking at things completely incorrectly? Is there a way of enforcing this that removes the burden from the user of the business logic? Thanks! Tim

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  • PHP ternary operator

    - by thecoshman
    ($DAO->get_num_rows() == 1) ? echo("is") : echo("are"); This dose not seem to be working for me,I get an error "Unexpected T_ECHO" I have tried it with out the brackets around the conditional. Am I just not able to use a ternary operator in this way? The $DAO-get_num_rows() returns an integer value. Thanks

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  • Java operator precedence guidelines

    - by trashgod
    Misunderstanding Java operator precedence is a source of frequently asked questions and subtle errors. I was intrigued to learn that even the Java Language Specification says, "It is recommended that code not rely crucially on this specification." JLS §15.7 Preferring clear to clever, are there any useful guidelines in this area? Here are a number of resources on the topic: JLS Operators JLS Precedence Java Glossary Princeton Sun Tutorial University of West Florida Usenet discussion Additions or corrections welcome.

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  • redefine __and__ operator

    - by wiso
    Why I can't redefine the __and__ operator? class Cut(object): def __init__(self, cut): self.cut = cut def __and__(self, other): return Cut("(" + self.cut + ") && (" + other.cut + ")") a = Cut("a>0") b = cut("b>0") c = a and b print c.cut() I want (a>0) && (b>0), but I got b, that the usual behaviour of and

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  • Regex AND operator

    - by user366735
    Based on this answer http://stackoverflow.com/questions/469913/regular-expressions-is-there-an-and-operator I tried the following on http://regexpal.com/ but was unable to get it to work. What am missing? Does javascript not support it? Regex: (?=foo)(?=baz) String: foo,bar,baz

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  • subscript operator on pointers

    - by Lodle
    If i have a pointer to an object that has an overloaded subscript operator ( [] ) why cant i do this: MyClass *a = new MyClass(); a[1]; but have to do this instead: MyClass *a = new MyClass(); (*a)[1];

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  • Using operator+ without leaking memory?

    - by xokmzxoo
    So the code in question is this: const String String::operator+ (const String& rhs) { String tmp; tmp.Set(this->mString); tmp.Append(rhs.mString); return tmp; } This of course places the String on the stack and it gets removed and returns garbage. And placing it on the heap would leak memory. So how should I do this?

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  • Operator precedence in scala

    - by Jeriho
    I like scala's propose of operator precedence but in some rare case unmodified rules may be inconvenient because you have restrictions in naming your methods. Is there in scala ways to define another rules for a class/file/etc? If not would it be resolved in future?

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  • how to call operator () in c++

    - by anish
    in c++ i have following code class Foobar{ public: Foobar * operator()(){ return new Foobar; } My quesion is how to call the (); if i do Foobar foo() the constructor gets called i am confused about behaviour of () can some explain me

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  • typedef and operator overloading in C

    - by jocapco
    Suppose I typedef an integer or integer array or any known type: typedef int int2 Then I overload operator * for int2 pairs, now if I initialize variables a and b as int. Then will my * between a and b be the overloaded * ? How do I achieve overloading an int and yet also use * for int the way they are. Should I create a new type?

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  • Where namespace does operator<< (stream) go to?

    - by aaa
    If I have have some overloaded ostream operators, defined for library local objects, is its okay for them to go to std namespace? If I do not declare them in std namespace, then I must use using ns:: operator <<. As a possible follow-up question, are there any operators which should go to standard or global namespace?

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  • Are there supposed to be more restrictions on operator->* overloads?

    - by Potatoswatter
    I was perusing section 13.5 after refuting the notion that built-in operators do not participate in overload resolution, and noticed that there is no section on operator->*. It is just a generic binary operator. Its brethren, operator->, operator*, and operator[], are all required to be non-static member functions. This precludes definition of a free function overload to an operator commonly used to obtain a reference from an object. But the uncommon operator->* is left out. In particular, operator[] has many similarities. It is binary (they missed a golden opportunity to make it n-ary), and it accepts some kind of container on the left and some kind of locator on the right. Its special-rules section, 13.5.5, doesn't seem to have any actual effect except to outlaw free functions. (And that restriction even precludes support for commutativity!) So, for example, this is perfectly legal (in C++0x, remove obvious stuff to translate to C++03): #include <utility> #include <iostream> #include <type_traits> using namespace std; template< class F, class S > typename common_type< F,S >::type operator->*( pair<F,S> const &l, bool r ) { return r? l.second : l.first; } template< class T > T & operator->*( pair<T,T> &l, bool r ) { return r? l.second : l.first; } template< class T > T & operator->*( bool l, pair<T,T> &r ) { return l? r.second : r.first; } int main() { auto x = make_pair( 1, 2.3 ); cerr << x->*false << " " << x->*4 << endl; auto y = make_pair( 5, 6 ); y->*(0) = 7; y->*0->*y = 8; // evaluates to 7->*y = y.second cerr << y.first << " " << y.second << endl; } I can certainly imagine myself giving into temp[la]tation. For example, scaled indexes for vector: v->*matrix_width[5] = x; Did the standards committee forget to prevent this, was it considered too ugly to bother, or are there real-world use cases?

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  • Query Performance Degrades with High Number of Logical Reads

    - by electricsk8
    I'm using Confio Ignite8 to derive this information, and monitor waits. I have one query that runs frequently, and I notice that on some days there is an extremely high number of logical reads incurred, +300,000,000 for 91,000 executions. On a good day, the logical reads are much lower, 18,000,000 for 94,000 executions. The execution plan for the query utilizes clustered index seeks, and is below. StmtText |--Nested Loops(Inner Join, OUTER REFERENCES:([f].[ParentId])) |--Clustered Index Seek(OBJECT:([StructuredFN].[dbo].[Folder].[PK_Folders] AS [f]), SEEK:([f].[FolderId]=(8125)), WHERE:([StructuredFN].[dbo].[Folder].[DealId] as [f].[DealId]=(300)) ORDERED FORWARD) |--Clustered Index Seek(OBJECT:([StructuredFN].[dbo].[Folder].[PK_Folders] AS [p]), SEEK:([p].[FolderId]=[StructuredFN].[dbo].[Folder].[ParentId] as [f].[ParentId]), WHERE:([StructuredFN].[dbo].[Folder].[DealId] as [p].[DealId]=(300)) ORDERED FORWARD) Output from showstatistics io ... Table 'Folder'. Scan count 0, logical reads 4, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Any ideas on how to troubleshoot where these high logical reads come from on certain days, and others nothing?

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  • Kernel panic on reboot after failed logical volume resize

    - by Derek
    I attempted to do a logical volume resize yesterday using the follwoing commands $sudo pvdisplay "/dev/sda8" is a new physical volume of "113.11 GiB" --- NEW Physical volume --- PV Name /dev/sda8 VG Name PV Size 113.11 GiB Allocatable NO PE Size 0 Total PE 0 Free PE 0 Allocated PE 0 PV UUID jwyO1o-b2ap-CW51-kx7O-kf26-arim-SM8V6m $sudo vgextend vg /dev/sda8 sudo vgdisplay vg --- Volume group --- VG Name vg System ID Format lvm2 Metadata Areas 2 Metadata Sequence No 9 VG Access read/write VG Status resizable MAX LV 0 Cur LV 5 Open LV 5 Max PV 0 Cur PV 2 Act PV 2 VG Size 131.74 GiB PE Size 4.00 MiB Total PE 33725 Alloc PE / Size 4769 / 18.63 GiB Free PE / Size 28956 / 113.11 GiB VG UUID AhusW2-pzFv-3W32-mpv2-s5VG-FN7S-kVSadx $sudo lvresize -L +20GB /dev/mapper/vg-var So as you can see, it looks like adding the physical volume to the vg worked, because i see free space available there. When I typed the lvresize command, it never returned. I let this run overnight in the background, but this morning I still couldnt successfully do a "pvdisplay" or "lvdisplay" because I think it was waiting on a lock or something, so the command never returned. When i went to log onto the server's console, I saw a bunch of messages like: rcu_sched_state detected stall on cpu 2 Now when I boot, I get a kernel panic error, and a message about not being able to mount /mapper/vg-root cannot open root device "mapper/vg-root" or unknown_block(0,0) Kernel Panic -not syncing: VFS: Unable to mount root file system on unknown_block(0,0) What should I do to get my system back up and running? Did I attempt to do the logical volume resize correctly? Thanks

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  • Am I running out of memory or do I have two logical drives instead of one

    - by user30904
    I did a complete reinstall of Ubuntu 13.04 a couple of months ago. Since then, I have switched out my motherboard with another. I kept the same hard drive. I just did an upgrade to 13.10. Recently, after this install, I keep getting the message that I'm running out of memory. I just checked my system usage and was surprised by what I found. I believed that I installed Ubuntu as a fresh install but when I check the system usage, it seems like there are two logical drives. I just did the basic install, so I was only expecting to see one partition but instead I see two. One is a small 300mb partition, the other is a 300gb partition I was expecting. Can anyone tell me if I have two partitions and/or logical drives and if so how I can fix this? I seem to have been running on the smaller drive and now I'm obviously out of space. I want to be able to use the bigger one at least.

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  • Union,Except and Intersect operator in Linq

    - by Jalpesh P. Vadgama
    While developing a windows service using Linq-To-SQL i was in need of something that will intersect the two list and return a list with the result. After searching on net i have found three great use full operators in Linq Union,Except and Intersect. Here are explanation of each operator. Union Operator: Union operator will combine elements of both entity and return result as third new entities. Except Operator: Except operator will remove elements of first entities which elements are there in second entities and will return as third new entities. Intersect Operator: As name suggest it will return common elements of both entities and return result as new entities. Let’s take a simple console application as  a example where i have used two string array and applied the three operator one by one and print the result using Console.Writeline. Here is the code for that. C#, using GeSHi 1.0.8.6 using System; using System.Collections.Generic; using System.Linq; using System.Text;     namespace ConsoleApplication1 {     class Program     {         static void Main(string[] args)         {             string[] a = { "a", "b", "c", "d" };             string[] b = { "d","e","f","g"};               var UnResult = a.Union(b);             Console.WriteLine("Union Result");               foreach (string s in UnResult)             {                 Console.WriteLine(s);                          }               var ExResult = a.Except(b);             Console.WriteLine("Except Result");             foreach (string s in ExResult)             {                 Console.WriteLine(s);             }               var InResult = a.Intersect(b);             Console.WriteLine("Intersect Result");             foreach (string s in InResult)             {                 Console.WriteLine(s);             }             Console.ReadLine();                        }          } }   Parsed in 0.022 seconds at 45.54 KB/s Here is the output of console application as Expected. Hope this will help you.. Technorati Tags: Linq,Except,InterSect,Union,C#

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