Why is using a Global Variables class (singleton) bad practise? The company I'm working for has a HUGE class (Globals.m) that is a singleton. It stores mostly a bunch of BOOLs that should go into NSUserDefaults, but there are also pointers to things like videoplayers that belong to various viewcontrollers. I am fairly new to iOS development (and I'm a lowly intern), but I know in my gut that the code smells to high heaven. How can I explain why using a singleton to store all the variables is bad?  Edit: I don't mean singletons are bad, I just mean in this case. Essentially every significant variable in the app is stored in this one instance.
What are drawbacks or disadvantages of singleton pattern? The  is a fully paid up member of the 's , but it lately seems rather orphaned by the developer world. I still use quite a lot of singletons, especially for , and while you have to be a bit careful about multithreading issues (like any class actually), I fail to see why they are so awful.  Stack Overflow especially seems to assume that everyone agrees that Singletons are evil. Why?  Please support your answers with "facts, references, or specific expertise"
How can I prove that $\frac{n^2}{x_1+x_2+\dots+x_n} \le \frac{1}{x_1}+ \frac{1}{x_2} +\dots+ \frac{1}{x_n}$? How can I prove that $\frac{n^2}{x_1+x_2+\dots+x_n} \le \frac{1}{x_1}+ \frac{1}{x_2} +\dots+ \frac{1}{x_n}$?   im trying to use AM-GM  $\sqrt[n]{ \frac{1}{x_1} \frac{1}{x_2} \frac{1}{x_3} ..\frac{1}{x_n}}   \le \sum_{k=1}^n \frac{{\frac{1}{x_1} +\frac{1}{x_2}+ \frac{1}{x_3}+ ..\frac{1}{x_n}}}{n}$  $ln\sqrt[n]{ \frac{1}{x_1} \frac{1}{x_2} \frac{1}{x_3} ..\frac{1}{x_n}} \le ln \frac{1}{n} \sum_{k=1}^n {\frac{1}{x_1} +\frac{1}{x_2}+ \frac{1}{x_3}+ ..\frac{1}{x_n}}$  $ \frac{1}{x_1} \frac{1}{x_2} \frac{1}{x_3} ..\frac{1}{x_n}\le  \sum_{k=1}^n {\frac{1}{x_1} +\frac{1}{x_2}+ \frac{1}{x_3}+ ..\frac{1}{x_n}}$  im not sure is this right or not, however i dont know how to include the $n^2$ in the nominator? is there also alternative proof using jensen inequality? Replacing Raster Values in Ras1 with Ras2 How to get around a problem with \usetikzlibrary{babel}? I am currently working on an update of tkz-euclide and new documentation but I just met the following problem. If I compile this code with pdflatex or lualatex and pgf 2.1 (The library babel does not exist with pgf 2.1) then the code compiles fine but with 3.0 pgf I must comment on the call \usetikzlibrary{babel} (pgf doc gives so I recommend to always load this library by saying \usetikzlibrary{babel}).  I'd like to know where the error occurred. Especially I would like to work around this problem.   With \usetikzlibrary{babel} I get the error Latex Error: ./untitled 2.tex:46 Undefined control sequence. l.1 \tkz@line@start  Bug in babel, bug in tikzlibrary{babel} bug in my code. I would like to keep  \usetikzlibrary{babel} but to avoid the error.  %!TEX TS-program = pdflatex \documentclass[a4paper]{article} \usepackage[french]{babel} \usepackage{tikz}  \usetikzlibrary{calc} %\usetikzlibrary{babel}  \makeatletter \pgfkeys{%     tkzdrawline/.cd,     start/.code         =  {\gdef\tkz@line@start{#1}},%     end/.code           =  {\gdef\tkz@line@end{#1}},%     start style/.code   =  {\tikzset{tkzstartstyle/.style={#1}}},%     end style/.code     =  {\tikzset{tkzendstyle/.style={#1}}},%    /tkzdrawline/.unknown/.code ={\let\searchname=\pgfkeyscurrentname\pgfkeysalso{%                          \searchname/.try=#1,/tikz/\searchname/.retry=#1}}}  %&lt;--------------------------------------------------------------–&gt; %                              Draw line %&lt;--------------------------------------------------------------–&gt; \pgfkeys{tkzdrawline/.cd, start/.code       =  {\def\tkz@line@start{#1}},% end/.code         =  {\def\tkz@line@end{#1}}, start style/.code =  {\tikzset{tkzstartstyle/.style={#1}}}, end style/.code   =  {\tikzset{tkzendstyle/.style={#1}}},   /tkzdrawline/.unknown/.code   = {\let\searchname=\pgfkeyscurrentname                                  \pgfkeysalso{\searchname/.try=#1,                                 /tikz/\searchname/.retry=#1}}}%         %&lt;--------------------------------------------------------------–&gt;  \def\tkzDrawLine{\pgfutil@ifnextchar[{\tkz@DrawLine}{%                                   \tkz@DrawLine[]}}%   \def\tkz@DrawLine[#1](#2,#3){%  \begingroup   \pgfkeys{tkzdrawline/.cd,start = {}, end = {}, start style={}, end style={},}   \pgfqkeys{/tkzdrawline}{#1}   \draw[ /tkzdrawline/.cd,#1] (#2) to%     node [at start,left,/tkzdrawline/.cd,tkzstartstyle] {\tkz@line@start}%     node [at end,right,/tkzdrawline/.cd,tkzendstyle] {\tkz@line@end} (#3);  \endgroup  }%   \makeatother   \begin{document}    \begin{tikzpicture}      \node (A) at (0,1) {};       \node (B) at (5,2) {};       \tkzDrawLine[end = {$\alpha$}](A,B)       \end{tikzpicture}  \end{document} What does protection from [quality] do? Example 1) Let's say I have some random creature with protection from white, and my opponent plays , a white card with the effect "Destroy all creatures." Can my creature with protection from white be destroyed by a white card that isn't actually targeting it specifically?  Example 2) I was playing a match with a friend where I had  on the field against his 3 zombies. Is he able to declare his zombies as blockers even though Elite Inquisitor has "protection" from zombies?  If he can declare them as blockers, does protection mean that no damage is dealt by the zombies to  Elite Inquisitor? Disk storage graphic and usage amount inconsistent? Sum of a power series $n x^n$ How to install packages in ubuntu without internet connection? macOS Sierra restarting download instead of resuming Find equation of a plane that passes through point and contains the intersection line of 2 other planes Find equation of a plane that passes through point P $(-1,4,2)$ that contains the intersection line of the planes  $$\begin{align*} 4x-y+z-2&amp;=0\\ 2x+y-2z-3&amp;=0 \end{align*}$$  Attempt: I found the the direction vector of the intersection line by taking the cross product of vectors normal to the known planes. I got $\langle 1,10,6\rangle$. Now, I need to find a vector normal to the plane I am looking for. To do that I need one more point on that plane. So how do I proceed? Is it proper usage to replace a comma in a list with a semi-colon in this situation (see details)? While writing a proposal at work today I needed to mention a list of things and within that list were multi-part items. It seems like replacing the comma with a semi-colon in this situation would make the sentence easier to understand, but is it correct usage?  With standard punctuation this could get confusing:       Some of my favorite things to do are   camping, playing football and   baseball, watching Laurel and Hardy   Movies, and traveling.   Proposed alternative. Is this acceptable usage?       Some of my favorite things to do are   camping; playing football and   baseball; watching Laurel and Hardy   Movies; and traveling. How can I prove the immigrant officers that I have significant ties in my home country?  Are there any documents that I need? What is the exact difference between fluid and responsive design? How can I send same email multiple times in iOS? I wanted to send a single email to different users. I save an email to drafts and send the email to a user and it goes to the sent box instead of staying in the drafts box. Is there a way I can send an email repeatedly from the drafts box? A term for words that change pronunciation with part of speech PHP: How do I loop through every XML file in a directory? For what values of $\alpha$, does this integral converge? For what values of $\alpha&gt;0$ this integral converges $$\int_0^{\infty} \frac {\sin x}{x^{\alpha}}dx $$ Badge icons missing in Achievements of mobile view The badge icon followed by the site icon in the Achievements dialog is missing in the mobile view. But the same is available in the full site view.  Screenshots for reference:  Achievements - Full site view:        Achievements - Mobile view: Possible Duplicate:          I installed the IE10 beta on Windows 7. It has an annoying autocorrect feature like the one in MS Word that messes up everything I write. How do I disable it? Copy complete structure of a table Using some methods, when you create a copy of a table you lose indexes, PK, FK, etc. For example in SQL Server I can say:  select * into dbo.table2 from dbo.table1;   This is just a simple copy of the table; all of the indexes / constraints are missing. How can I copy a table structure (without using a backup)?  I am primarily looking to do this manually, but if that's not possible I'll accept any solution. Hi I am working on a website for a student organization of my college.  In order to prevent spams, I have been looking for ways to limit account applicants only with email addresses from the college but haven't figure out how