passing Temporary variables to reference arg in Constructor works. but not for functions in general. Why? Consider the following code. Here, A a(B()) compiles even though the constructor is A(B&amp; b); But print(B()) does not work. But print is also declared as print(B&amp; b); Why this inconsistency?  #include &lt;iostream&gt; using namespace std;  class B{     public:             char b; };  class A {     public:             B b;             A(B&amp; b);             A() { } };  A::A(B&amp; b) {     this-&gt;b = b; }  void print(B&amp; b) { }  int main(){     print(B());     A a(B()); }
Default constructor with empty brackets Is there any good reason that an empty set of round brackets (parentheses) isn't valid for calling the default constructor in C++?  MyObject  object;  // ok - default ctor MyObject  object(blah); // ok  MyObject  object();  // error   I seem to type "()" automatically everytime. Is there a good reason this isn't allowed?
Does a finite $[E:K]_s$ imply that $[E_s:K]$ is finite? Let $E/K$ be an algebraic extension of fields and denote by $E_s$ the separable closure of $K$ in $E$, i.e. the set of all elements of $E$ that are separable over $K$ (which can be shown is a (separable) subfield of $E$).  I would like to show that the implication     $\left[E:K\right]_s &lt; \infty \implies \left[E_s:K\right] &lt; \infty$   holds, where $\left[E:K\right]_s$ denotes the separable degree of $E/K$ and $\left[E_s:K\right]$ the 'ordinary' degree of $E_s/K$.  In the textbook I am learning with, it is said that one could use the Primitive Element Theorem to do this, but I would also be fine with any other approach, as long as it's not getting too fancy and staying in the realm of 'common' textbook theorems known when dealing with separable extensions (and I didn't see how the Primitive Element Theorem would help).  This is not my focus (I want to write a Bachelor's thesis about polynomial factorizing elements of $\mathbb{Z}[X]$), but I'm in the process of reading into commutative algebra after about 1.5 years break from it.  My idea was something like assuming $\left[E_s:K\right] &lt; \infty$ and $\left[E_s:K\right] = \infty$ to construct infinitely many $K$-homomorphisms $E_s/K \longrightarrow C/K$, where $C$ is some algebraic closure of $E_s$, which would then contradict $\left[E_s:K\right]_s = \left[E_s:K\right] &lt; \infty$. Of course, an infinite basis would yield infinitely many $K$-vector space homomorphisms, but getting (infinitely many) ring morphisms seems to by an entirely different ting (unsurprisingly so...). Thought of using something like     Given two roots of the minimal polynomial of one of the infinitely many elements of a $K$-basis of $E_s/K$, there is a $K$-morphism $E_s/K \longrightarrow C/K$ that sends one to the other.   but this didn't seem very fruitful. I admit I haven't spent hours on this, I just didn't get very far and should focus on moving on, while still getting an answer on the 'howto' along the road would be really nice. This is a doubt from Milnor's "Topology from a Differentiable Viewpoint".     For a smooth $f:M\to N$, with $M$ compact, and a regular value $y\in N$, we define $n(f^{-1}(y))$ to be the number of points in $f^{-1}(y)$. It is easy to see that $n(f^{-1}(y))$ is finite. It can also be seen that $n(f^{-1}(y))$ is locally constant; i.e. there is a neighbourhood of $y$ such that for every point $y'$ in that neighbourhood, $n(f^{-1}(y'))=n(f^{-1}(y))$.   The proof for the statement in bold is the following:     Let $x_1,x_2,\dots,x_n$ be the points of $f^{-1}(y)$, and choose disjoint neighbourhoods $U_1,U_2,\dots,U_n$ of these points, which are mapped diffeomorphically into neighbourhoods $V_1,V_2,\dots,V_n$ of $y$. The required neighbourhood is $(V_1\cap V_2\cap\dots V_n)-f(M-U_1-U_2-\dots U_n)$.   I don't understand how $(V_1\cap V_2\cap\dots V_n)-f(M-U_1-U_2-\dots U_n)$ is open. I know that $(V_1\cap V_2\cap\dots V_n)$ is open. However, how can one prove that $f(M-U_1-U_2-\dots U_n)$ is closed? I can see this working if $f$ is surjective, but not otherwise. Is it possible to create matter? Is it possible to create matter? In a recent discussion I had, it was suggested that with enough energy in the future, "particles" could be created.   It seems like this shouldn't be possible due to conservation but perhaps I could be wrong. Would any of you Physics masters care to elaborate?  (Note... I will understand the basics, I am by no means an expert.) How do I uninstall the command line tools for Xcode? We have a bunch of Mac at work that no longer require Xcode or command line tools so we'd like to remove them so the compilers aren't hanging around and we don't have to keep updating them when updates arrive. , but now that Xcode is an app store app you are left with the tools if you ever install them. Can we clean this other than wiping the OS for macs running 10.10 and newer? write data line by line on iphone Started new job. Rollover previous employer 401k to new 401k, IRA or Roth IRA? I am not asking about the two factor authentication process where the user needs to enter both a password and a one-time-password.  Gmail recently (I don't know from when exactly) changed their login process which is depicted in the following screenshot:     So, the new steps are as follows:   Enter email   Click Next  Enter password   Click Sign In    as opposed to the previous and usual way of logging in:   Enter email and password   Click Sign In    Isn't the new process non-user friendly requiring extra user interactions?  Since, Google does not usually make UX blunders can you explain the reasoning behind the new process? I'm looking for details like user interaction simplicity or any other hidden advantages.  Note: The question  doesn't cover the reason behind the change while Mervin Johnsingh's answer cites Google's reason. Do Chinese citizens require a visa to go to Hong Kong for less than 7 days? Recently the keyboard and trackpad on my 2015 13" MacBook Pro have stopped working. This is the second laptop to do this, the same issue happened about 6 months ago and Apple gave me a new one when they could not figure it out.  The issue usually starts with force touch not working then progresses to the keyboard and trackpad not being recognized at all. Currently the power button works and force touch works but all other keys and the trackpad don't work.  When this happens there are a lot of errors in the console regarding the AppleHSSPIController.  4/21/16 6:56:47.000 AM  kernel[0]   Error: AppleHSSPIDevice::start failed to get device descriptor 4/21/16 6:56:47.000 AM  kernel[0]   Error: AppleHSSPIController::_enumerateDevice Start failed 4/21/16 6:56:47.000 AM  kernel[0]   Error: AppleHSSPIController::_handleEnumerationFailureGated Giving up on device   You can see the full log here: Guest (not logged in) users can only sort questions with specific tag by newest I think this is platform wide (all SE sites).   Logout Choose a tag, eg.  on SO Try to sort questions by something other than newest   No matter what sorting is chosen, questions are sorted by newest Why can't a single photon produce an electron-positron pair? In reading through old course material, I found the assignment (my translation):     Show that a single photon cannot produce an electron-positron pair, but needs additional matter or light quanta.   My idea was to calculate the wavelength required to contain the required energy ($1.02$ MeV), which turned out to be $1.2\times 10^{-3}$ nm, but I don't know about any minimum wavelength of electromagnetic waves. I can't motivate it with the conservation laws for momentum or energy either.  How to solve this task? is a wonderful freeware Windows swiss-army-knife for image viewing &amp; editing.  For me, the key features are fast viewing, simple editing (crop, contrast, brigthness, rotation, resampling), file operations (delete, copy to folder) and extended image information access (exif data) combined in the same interface. Versatile batch jobs are a very nice bonus.  But unfortunately IrfanView is for Windows only, and isn't . What would be the nearest equivalent for linux? How to reinstall Cortana? With reference to:    I removed the Cortana packages from my running Windows 10 using the method posted by magicandre1981 and using  win6x_registry_tweak.   My question is how can I re-install Cortana (or for that matter any other package removed similarly)?  I have opened up the install.wim image (converted from a Win 10 install.esd file) and found Cortana in the system apps folder, but don't know how / what to use to re-install it.  Any help please? How can author deal with late reviews? Another problem I personally struggle with in peer-review publication process is the situation when review takes really, really, really long. The precise definition of "long" is probably very area-specific: for example a paper in Maths will probably took longer to review than one in Physics. Many well-established journals and major publishers, sadly, prefer not to specify the "rules of the game" precisely, particularly how long the review process should normally take. Fortunately, I quite often serve as a referee with the very same journals and know the amount of time I am given to write a review. Unfortunately, when I am an author, I do not observe these deadlines to be always met. For example, a notable U.S. publisher would ask a reviewer to send a review in 2 months; but in practice a first review of my paper once took as long as 8 months.  As a rule of thumb, I usually start writing to editors with questions about "the status of my paper" in X+1 months time, when X is a deadline time for a reviewer to submit a review. This strategy is not particularly successful &mdash; what I usually get is a recommendation to be more patient. Since there is no "official" deadline time announced, there is no formal ground for complaints here.  Of course, such delays lead to a whole bunch of funny situations, particularly if a preprint is put online (e.g., on arXiv) and the results are presented in some conferences. Follow-ups with no official paper to cite, grant applications in which you can not justify by a solid publication, good research but bad bibliometrics or CV, to name just a few.   Could you recommend an efficient way to deal with this problem? Is "shined" correct? If so, is "he shined X on the tree" also correct? Recently, I overhead a former professor of mine use the word shined, a word that makes me grammatically uncomfortable.  She used it as following: "Then, after we shined a light on the other ball, what happened?..."  My first question is: Is using shined mainstream, over what sounds better to my ear, shone?  If so, is there any historical flip-flopping between the two usages?  Secondly, if shined is in fact legit, can it be used transitively?  Saying something like,      The light shined all throughout the night.   while odd, doesn't sound as bad to my ear as,     He shined the light on the ball throughout the night.   The latter sounds quite bad to my ear.  Indeed, à propos the original question, can shone &mdash; the better sounding alternative to my ear &mdash; be used transitively? Reset Windows 10 from USB I have a Windows machine (laptop) that needs fixing. The current installation is really badly broken (e.g. the taskbar is unresponsive, but the Explorer windows work, booting takes literally half an hour) and when I try to access the settings app and click on the tile to access the reset settings it instantly crashes. The same happens in Safe Mode.  I have created a USB install medium using the tool offered by Windows on my own Windows desktop machine. I've ensured that both the laptop and the USB tool have the same version of Windows (Home, 64-bit, NL). When I want to reinstall Windows on the laptop with this stick I am asked to enter a serial number which I obviously don't have. I don't want to try and see if I can phone activate it, because if it fails the install is gone.  I need to reinstall this Windows machine from a USB stick. There are a few problems I can't find an immediate solution for on the .   If I use a tool such as  to extract the serial number, will this work? If the above does not work, how can I reinstall this Windows machine? I got a stomach flu or I got the stomach flu or I got stomach flu? "debconf: DbDriver "config": config.dat is locked by another process: Resource temporarily unavailable" while installing packages How to detect online/offline event cross-browser? Prove the following $A \setminus (B\setminus C) = (A\setminus B)\cap (A \cup C)$ I want to prove the following so I decide to rewrite the RHS  $$A \setminus (B\setminus C) = (A\setminus B)\cap (A \cup C)$$ $$ A\setminus(B\setminus C) = A\setminus (B \cap C^c) = A\cap (B\cap C^c)^c = A\cap(B^c\cup C) = (A\cap B^c)\cup(A\cap C) $$ there is way that $(A\cap B^c)\cup(A\cap C)\rightarrow (A\setminus B)\cup(A\cap C) = (A\setminus B)\cap (A \cup C)$?  thanks. EDIT  LHS: $$x\in A \vee x\in A\cap C \rightarrow x\in A \wedge x\in C$$ RHS: $$x\in A \wedge x\in A\cup C \rightarrow x\in A \vee x\in C$$  how it can help me?