Understanding C#'s Type converting I don't understand why this doesn't work:  Classes:  public abstract class BaseObj {      public bool IsValid =&gt; GetValidationErrors().Count == 0; }  public class BaseObjWithId: BaseObj  {     public int Id { get; set; } }  public class BaseReference&lt;T&gt; : BaseObj where T : BaseObjWithId {      public T ObjReference { get; set; }  }  public class Foo: BaseObjWithId {     public string Name{get;set;} }  public class FooRef : BaseReference&lt;Foo&gt; {  }   Code-Statement:      BaseReference&lt;BaseObjWithId&gt; foo= new FooRef();      Error CS0029  Cannot implicitly convert type...   This works:      BaseReference&lt;Foo&gt; foo= new FooRef();   But I don't understand why, because Foo is a BaseObjWithId...  Thank you for your explanation
In C#, why can't a List object be stored in a List variable It seems that a List object cannot be stored in a List variable in C#, and can't even be explicitly cast that way.  List&lt;string&gt; sl = new List&lt;string&gt;(); List&lt;object&gt; ol; ol = sl;   results in Cannot implicitly convert type System.Collections.Generic.List&lt;string&gt; to System.Collections.Generic.List&lt;object&gt;  And then...  List&lt;string&gt; sl = new List&lt;string&gt;(); List&lt;object&gt; ol; ol = (List&lt;object&gt;)sl;   results in Cannot convert type System.Collections.Generic.List&lt;string&gt; to System.Collections.Generic.List&lt;object&gt;  Of course, you can do it by pulling everything out of the string list and putting it back in one at a time, but it is a rather convoluted solution.
Find all positive integers $n$ such that $n$ is divisible by all the positive integers less than or equal to $\sqrt{n}$ Find all positive integers $n$ such that $n$ is divisible by all the positive integers less than or equal to $\sqrt{n}$  My thought: If n is a positive integer, let d(n) denote the number of positive divisors of n and I will find n such that $d(n) \ge 2\sqrt{n} - 1$ Pre-generate Review audits to avoid the lag? Practical way to implement prevention of IP Spoofing I am an undergraduate Computer Science student and was hoping to gain some knowledge of ways to help prevent IP spoofing but all the resources I have tried out elaborate this concept in a theoretical way. I want to try out my hands at one of the techniques like:      How do I simulate this whole situation in my own system were I myself am the attacker and I myself have to defend it? And once I have gained an understanding of it, then how do I start translating that into programming terms? This integral is very closely related to the sophmores dream that states  $$ \int_0^1 x^{-x}\mathrm{d}x = \sum_{n=1}^\infty n^{-n} = 1.27\ldots $$  For example here   Now I want to bound the integral, and showing that is less that 2.  For the interval $[0,1]$ a good bound is rewriting it to $\exp(x\log x)$ and using the expansion   $$ 1 - x \log(x) + \frac12 (-x \log(x))^2$$  but how does one handle $[1,\infty)$ ? In this answer here     gives bounds to the integral, but they are not tight enough.. So to taste my question again, how does one prove that   $$ \int_0^\infty \frac{\mathrm{d}x}{x^x} \leq 2 $$ Is there such a thing as a line/vertices symbology? If not a workaround? In some situations, particularly when editing, I would like to see my lines as well as all the vertices similar to the effect I get when using the Edit Vertices tool but on all features in the feature class not just the selected feature.  The solution should be dynamic, without having to create a separate point layer but having one line features class loaded twice in the TOC is acceptable.  Programmatic solution using an example (addin, ArcObjects &amp; VB.Net) is acceptable.  I have the ArcEditor license in case there is a trick to use with representations. Disable COPY drag and drop in Windows Explorer in Windows 7 I am trying to determine if the sum $\sum_{n=1}^\infty \frac{n+4^n}{n+6^n}$ is convergent or divergent.   In attempting to solve this problem I began by seeing if I could do the divergence test - in this case it is not helpful. The terms $4^n,6^n$ look like geometric series type terms but the $n$ in the numerator and denominator are troublesome. I first tried factoring $n$ out of the expression:  $$\sum_{n=1}^\infty \frac{n+4^n}{n+6^n} = \sum_{n=1}^\infty \frac{1+\frac{4^n}{n}}{1+\frac{6^n}{n}}$$  Next I tried comparing to the series $$\sum_{n=1}^\infty \frac{\frac{4^n}{n}}{\frac{6^n}{n}} = \sum_{n=1}^\infty \frac{{4^n}}{{6^n}} = \sum_{n=1}^\infty{\left(\frac{2}{3}\right)}^n$$  This is a convergent geometric series as $r = \frac{2}{3}\lt1$  now I reason that the series $\sum_{n=1}^\infty \frac{1+\frac{4^n}{n}}{1+\frac{6^n}{n}}$ is neither smaller not greater than the series $\sum_{n=1}^\infty{(\frac{2}{3})}^n$ Am I able to conclude anything in this case by a direct comparison test or can I only conclude that the first series is convergent if the second is greater than the first?  Thanks Often in my papers I want to mention theorems in the introduction that are introduced in more detail and proved in a later section.  I'd like to include the statement of these theorems twice over, each time numbered as the theorem would naturally appear in its later section.  My current solution (using amsthm) is, e.g.  %(in the introduction) \newtheorem*{thm:associativity}{Theorem \ref{thm:associativity}} \begin{thm:associativity} Lorem ipsum ... \end{thm:associativity}  %(in a later section) \begin{thm} \label{thm:associativity} Lorem ipsum ... \end{thm}      Can anyone think of a cleaner solution? What are the advantages of 10-bit monitors? To support 10-bit color the following are needed:   A monitor supporting it. A GPU supporting it (only AMD FirePro and NVIDIA Quadro support this?). Compatible software. Unless I am mistaken there are very few programs out there supporting 10-bit color. Photoshop is a notable example.   The questions are about how 10-bit monitors perform in comparison with 8-bit monitors:   In which situations would a 10-bit monitor give a noticeable advantage over an 8-bit monitor (say, for professional photography)? Have 10-bit monitors been compared against 8-bit monitors based on subjective or objective tests? What were the results? Human eyes can see only 10m colors, so would using a monitor with 1b colors make a difference? When is the finalize() method called in Java? Why didn't the Ministry use owls to find Sirius? Harry, before the Triwizard Tournament, was able to send owls to Sirius when he was in hiding (not at Grimmauld Place) just by telling them "just find him, will you?", and the owl would come back a few days later with an answer. This doesn't happen with Hedwig only, because, if I recall correctly, he uses school owls as well.  If finding Sirius was as easy as telling an owl "find him", and a 13-year-old wizard could do it, how come the Ministry had no clue as to where he was? They could've sent an owl with a summons and followed it from a distance.  Two theories, neither mentioned in the book, and both a bit unlikely:   He was living as a dog and -hopefully- the Ministry would not be able to recognize him. Unlikely because the owl would have got there anyway, so they would have guessed the dog was Sirius in disguise, not necessarily as an animagus, but maybe he could perform human-animal transfiguration (remember he was brilliant at school).. Kingsley Shacklebolt was already in charge of the hunt and Dumbledore told him Sirius was innocent and all that. Then, Kingsley would have prevented the Ministry from using any method that could've actually worked. Unlikely because they could've used owls before Dumbledore's tip, when Kingsley didn't know Sirius was innocent, and also because Kingsley was quite powerful and had the support of Crouch and others at the Ministry, so if he was in charge, they would probably have succeeded.   Your thoughts? Why use hex? Hey! I was looking at this code at   I noticed that in some situations they used hex numbers, like in line 134:  for (j = 1; val &amp;&amp; j &lt;= 0x80; j &lt;&lt;= 1, q++)   Now why would they use the 0x80? I am not that good with hex but I found an online hex to decimal and it gave me 128 for 0x80.  Also before line 134, on line 114 they have this:  small_n = (n &amp; 0xffff0000) == 0;   The hex to decimal gave me 4294901760 for that hex number. So here in this line they are making a bit AND and comparing the result to 0??  Why not just use the number? Can anyone please explain and please do give examples of other situations.  Also I have seen large lines of code where it's just hex numbers and never really understood why :( Are omniscience and omnipotence mutually inconsistent? I see this in The God Delusion by Richard Dawkins:       If God is omniscient, he must already know how he is going to intervene to change the course of history using his omnipotence. But   that means he can't change his mind about his intervention, which   means he is not omnipotent.   Is this argument sound? My advisor wants me to include a name of someone who has no contribution to the paper My first advisor wants me to include my second advisor's name in a paper that I worked on before she (2nd advisor) came along.   Should I include her name even though she didn't do anything in that paper? I don't think she even read it. How to disable notifications for a single mailbox in Mail? When managing multiple mailboxes, is it possible to disable the notifications for certain mailboxes? Efficiently storing query-affecting settings in a database I want to know how to efficiently store query-affecting settings in a large analytical database (MS SQL Server). By efficiency I mean no hardcode (1) and fast/optimal query processing (2).  My example  I've got a massive table of sales orders. Let's simplify it to two columns:  SalesOrder  OrderID      int      Primary Key  OrderDate    date   I need to retrieve the list of orders for the last X days and this X should be configurable. That's why I introduce a table of settings where I define it:  Admin_Configuration  SettingName   (PK)|      SettingValue  ------------------|------------------  DaysBack          |          30      It allows me not to hardcode this "30" in query definitions. Then I would run queries like:  SELECT OrderId   FROM SalesOrder as S   JOIN Admin_Configuration as A     ON A.SettingName = 'DaysBack'   WHERE [OrderDate] &gt; DATEADD(DAY, -A.SettingValue, GETDATE());   Performance  It avoids hardcoding, but leads to a performance problem. This query runs much slower than it would've, had I simply hard-coded 30 in the WHERE clause.  My understanding is that optimizer doesn't know how large my SettingValue is and assumes the worst - that all rows would be retrieved from the SalesOrders table, thus leading to a suboptimal query plan.  Trying a scalar function yielded even worse results. I'm desperate enough to have a separate view which stores these hardcoded settings but I've been refraining from it with hopes for a better solution.  Here is the original query plan (with a join): 4 seconds elapsed   Here is the plan with subquery, as :  SELECT orderid FROM [SalesOrder] as s WHERE s.OrderDate &gt; dateadd(DAY,    (SELECT -NumValue    FROM Admin_Configuration where SettingName = 'DaysBack'   )     , getdate())   7 seconds elapsed, slightly slower   As for the ideal performance: I just hardcoded 20, the query took 2 seconds. It needs mentioning that the Admin_Configuration table contains only 18 rows, hence it shouldn't affect performance.  SELECT OrderId   FROM SalesOrder as S   JOIN Admin_Configuration as A     ON A.SettingName = 'DaysBack'   WHERE [OrderDate] &gt; DATEADD(DAY, -20, GETDATE());   Using parameters would mean that I'd have to replace views (that I use now) with stored procedures/table-valued functions, which is unacceptable in my case I've found ,  and  which are releated to my question, but no longer seem to apply since Drupal 8.1 and the deprecation of .  Also popular guides such as  appear to no longer apply as they also mention composer manager.   The other solution opposed to composer manager, alter the core composer.json file feels like too much core hacking and would probably break with every Drush update of Drupal core(?).  More specifically, I am attempting to update  from Drupal 7 to 8. I have created my composer.json file as follows:  {   "name": "drupal/views_vcards",   "description": "Allows creation of vCards using the fields provided by the Views module.",   "type": "drupal-module",   "license": "GPL-2.0+",   "homepage": "https://drupal.org/project/views_vcards",   "require": {     "maennchen/zipstream-php": "0.3.*"   } }   But if I put a composer.json file in my module folder, how do I make Drupal aware that that file is there, and how do I make sure the required zipstream-php library is downloaded?  Simply running composer update from the Drupal root does update a lot of Drupal dependencies, but it does not include the composer.json files that are in the modules folders. I also don't assume I should be calling composer install from inside all modules with dependencies.  How do I make Drupal aware of a module's dependency without using composer manager and/or hacking core?  UPDATE:  The  appears to have support a wildcard path:  {     "require": {         "wikimedia/composer-merge-plugin": "dev-master"     },     "extra": {         "merge-plugin": {             "include": [                 "composer.local.json",                 "extensions/*/composer.json" // &lt; ---- THIS LINE             ],             "require": [                 "submodule/composer.json"             ],             "recurse": true,             "replace": false,             "merge-dev": true,             "merge-extra": false         }     } }   Why doesn't core merge modules/*/composer.json, that would solve everything right?  Update 2:  THe reasoning for not supporting this is covered in  (which also has been quiet for some time now). Do compound subjects like "everyone ... and everyone..." take singular or plural verb agreement? Here are the examples of compound subjects:      Everything on the bed and everything in the closet was organised   in under an hour.   Everybody who witnessed the shooting and everybody   in the room were interviewed.   Anyone on the soccer team and   anybody on the basketball team was eligible for the scholarship.   Should I also use was instead of were in the second example? Or the first and the third examples are incorrect that I should use were instead of was. Basic Web Development IDE/Editor like Dreamweaver? I've used Windows for many years, using Dreamweaver as my editor as it had a file tree which is based on a project (via Local, FTP or SFTP).  I need a web development IDE with the following functionality:   syntax highlighting for PHP, HTML, CSS, JavaScript  file tree - Local, FTP, SFTP, Project-Based (e.g. via the methods of Local/FTP/SFTP) in other words, like Dreamweaver can open multiple files (tabbed)   Additionally, I wouldn't mind features like debugging, class listings, etc, as long as I can hide them away. Word or Phrase for "Easily Swayed" What word or phrase best communicates the idea that a human (or other sentient being) is easily swayed, particularly between moral good and evil? Words I have found that are close are:   Impressionable - Easily influenced because of a lack of critical ability.   Implies that the subject lacks critical skills, and misses the concept of good and evil.  Gullible - Easily persuaded to believe something   Misses the concept of good and evil    I created a typical angels and demons scenario to demonstrate the polar extremes of the the spectrum. In this scenario, I lack the word to describe the humans, who can be influenced towards either end of the spectrum if impressed upon by an external entity.     The angels are devoted to good, and are immovable in their ideals. The demons are wicked, and will feign morality only to manipulate others. Both prey upon the humans, who are ____________.   I think that the key here is the spectrum of good an evil. Here are examples of other spectra and their associated words, for comparison.   Easily pushed from calm to angry: Temperamental Easily moved from determined to hopeless: Weak-willed Easily influenced by propaganda: