What is the Serialization Proxy Pattern?
Follow up: instance control in Java without enum
In MySQL 5.0 why does the following error occur when trying to create a view with a subquery in the FROM clause?     ERROR 1349 (HY000): View's SELECT contains a subquery in the FROM clause   If this is a limitation of the MySQL engine, then why haven't they implemented this feature yet?  Also, what are some good workarounds for this limitation?  Are there any workarounds that work for any subquery in the FROM clause or are there some queries that can not be expressed without using a subquery in the FROM clause?    An example query (was buried in a comment):  SELECT temp.UserName  FROM (SELECT u1.name as UserName, COUNT(m1.UserFromId) as SentCount        FROM Message m1, User u1        WHERE u1.uid = m1.UserFromId        Group BY u1.name HAVING SentCount &gt; 3 ) as temp I presented the following problem to some of my students recently (from Senior Mathematical Challenge- edited by Gardiner)  In the Fibonacci sequence $1, 1, 2, 3, 5, 8, 13, 21, 34, 55,\ldots$ each term after the first two is the sum of the two previous terms. What is the sum to infinity of the series: $$\frac{1}{2} + \frac{1}{4}+ \frac{2}{8} + \frac{3}{16} + \frac{5}{32} +\frac{8}{64} + \frac{13}{128} +\frac{21}{256} +\frac{34}{512}+ \frac{55}{1024} + \cdots$$  Now, I solved this using an infinite geometric matrix series (incorporating the matrix version of the relation $a_n= \frac{a_{n-1}}{2}+ \frac{a_{n-2}}{4}$), and my students, after much hinting on my part, googled the necessary string to stumble across Binet's formula (which allows one to split the series into two simple, if rather messy, geometrics). Both of these are good methods, but neither really seems plausible for a challenge set for 15-18 year olds under exam conditions. So how is one supposed to do it? "You just can't" vs. "you can't just " I'm a bit confused about this. Which expression is correct?     You can't just do that.    or      You just can't do that.   I'm trying to say:     You can't just bash an ideology because of what someone has said/done. Can any one help? I purchased a solar powered PIR security light, with the intention of putting it inside my kitchen window. The PIR would be inside the window, but this does not work.  When I go outside to activate the light, it does not work. When I go inside to run my hand across the sensor, it works.  Will a PIR unit penetrate glass, or am I barking up the wrong tree? Show $\frac{a_{1}+...+a_{n}}{b_{1}+...+b_{n}}$ is between the smallest and largest fraction $\frac{a_{i}}{b_{i}}$, where $b_{i}&gt;0$.  Attempt  Assume the largest is $\frac{a_{n}}{b_{n}}\Rightarrow$  $\frac{a_{n}}{b_{n}}-\frac{a_{1}+...+a_{n}}{b_{1}+...+b_{n}}\Rightarrow $  $\frac{b_{1}+...+b_{n-1}}{{b_{1}+...+b_{n}}}[\frac{a_{n}}{b_{n}}-\frac{a_{1}}{b_{1}+...+b_{n-1}}-...-\frac{a_{n-1}}{b_{1}+...+b_{n-1}}]\Rightarrow $  if $a_{1}&lt;0$, $w=\frac{a_{n}}{b_{n}}-\frac{a_{1}}{b_{1}+...+b_{n-1}}-...-\frac{a_{n-1}}{b_{1}+...+b_{n-1}}&gt;\frac{a_{n}}{b_{n}}-\frac{a_{2}}{b_{1}+...+b_{n-1}}-...-\frac{a_{n-1}}{b_{1}+...+b_{n-1}}$  any hints or solutions? Is there any intuition or meaning regarding Cauchy-Riemann equations? Are the LIGO observations proof of a black hole merger, and what happened to the black holes? What are the restrictions on the use of Slayer's Prey? In the recent book Xanathar's Guide to Everything, there are some subclasses/archetypes added for Rangers, among them the  (p. 43), which gives some specific helpful features. Hunter's Sense  At 3rd level, you gain the ability to peer at a creature and magically discern how best to hurt it. As an action, choose one creature you can see within 60 feet of you. You immediately learn whether the creature has any damage immunities, resistances, or vulnerabilities and what they are. If the creature is hidden from divination magic, you sense that it has no damage immunities, resistances, or vulnerabilities. You can use this feature a number of times equal to your Wisdom modifier (minimum of once). You regain all expended uses of it when you finish a long rest.  The limitations on use are clearly spelled out. Slayer's Prey  Starting at 3rd level, you can focus your ire on one foe, increasing the harm you inflict on it. As a bonus action, you designate one creature you can see within 60 feet of you as the target of this feature. The first time each turn that you hit that target with a weapon attack, it takes an extra 1d6 damage from the weapon. This benefit lasts until you finish a short or long rest. It ends early if you designate a different creature.  So from this, I would interpret it as it being able to switch from creature to creature at will, but there is no guidance as to what happens if the creature under the mark dies, or if you can carry it (so to speak) from encounter to encounter. Is there a limitation on the use of Slayer's Prey in the wording that I am missing? Or is this a basically a multiple use feature? (i.e., you can designate any creature as a bonus action, with no limitations on uses per day)? The extra d6 seems a little overpowering at lower levels, and somewhat meh at higher levels. FWIW, the GM basically allowed it as multi-use for the session, and was going to also try to find clarification. Salesforce Internal Server - What's in a GACK? Background  I have been working with Salesforce Support for several weeks now trying to get them to escalate an internal server error with GACK 2134764861-123797 (1611479512) (1611479512). After a long period of waiting I was told that in order to escalate quickly they needed to reproduce the issue in a controlled way. This was again taking them a considerable amount of time so I created a reduced test case myself () that concisely reproduces the issue with a very small amount of code. I was told that this wasn't a valid reproduction because it caused a different GACK (1291518605-518052 (1659192199) (1659192199)) despite reproducing the exact same user experience.  My Question  What makes up a GACK? Is there any information that I can take from their structure that can give me clues on which errors are related without access to the full back-end tools that Salesforce Support uses? It is not infrequent that without premier support it takes me upwards of two weeks to escalate platform bugs and I am hoping that I can somehow use the information from the GACK to reduce this time. The popup when you click on your newest badge in your user profile has a &quot;Learn more&quot; button, but its alignment is suboptimal; it's too close to the top of its container:  It looks better with a 4px top margin: Post for clarifications on the updated pronouns FAQ In what order should one apply max HP reduction and damage? A character at 10/26 HP is hit by a Wraith and fails the Constitution saving throw. They take 21 damage and their maximum HP is reduced to 5.  Are they unconscious because the 11 excess damage is less than 26 or dead because it's greater than 5? glBufferData not working outside main function Find Items in one column that are not in another column I have two columns in Excel, and I want to find (preferably highlight) the items that are in column B but not in column A.   What's the quickest way to do this? What is the function represented by the power series $$ \sum_{k=2}^\infty\frac{x^k}{k(k-1)}\quad? $$  It looks like $\dfrac1{1-x}$ but I don't know. What are the use cases for different scoping constructs? My keyboard is typing by itself, could there be a ghost in it? The keyboard on my laptop seems to be typing by itself:   It sometimes types characters like 134, whether by itself or when I hit certain keys. Repeating characters may appear unexpectedly. The system volume may change by itself, or windows like the Print dialog or Web browser may appear.   This can happen without any input or as I type, and may occur more often when certain keys are pressed. Sometimes, the keyboard fails to respond altogether. This is happening regardless of the software involved.  Is there a ghost in my keyboard—is my keyboard broken?  A sample of text from the keyboard might look like this (normal QWERTY...ASDF...ZXC... sequence is expected):   QWERTYUIOPASDF)(G@*HKLZXCVBN QWERTYIOPASDFGL!#ZXCVB13 QWERTYUIOPASDFGHJKLZXCVB!#N qwertyu41iopasdf19g13h28j113k4113zxcvb4n qwerty4u1iopasdf0g7h1jklzxcvb13m qwert13uuuuuuuuuuuuuuuiopasdf87091134ghhhhhhhhhhhhhhhhhhhhhhh13jk13zxcvb14      This question comes up often and the answers are usually the same. This post is meant to provide a definitive, canonical answer for this problem. Feel free to edit the answer to add additional details. How can I change the default "ens33" network device to old "eth0" on Fedora 19? How do constant aperture zoom lenses work? Gauss's law not making sense If we have a point charge and outside of it we have a non-conducting Gaussian sphere, then Gauss's law says that the net flux should be zero. I agree that the total field lines coming in are equal to the number of field lines coming out, but isn't it true that the magnitude of the electric field at those segments of the sphere where the field is coming in is greater than those where it is coming out? So when we integrate, wouldn't these areas, having a greater electric field, contribute more to the net flux? I don't see why they would cancel each other out.