equivalence

问题 In database theory, what is the difference between "conflict serializable" and "conflict equivalent"? My textbook has a section on conflict serializable but glosses over conflict equivalence. These are probably both concepts I am familiar with, but I am not familiar with the terminology, so I am looking for an explanation. 回答1: Just two terms to describe one thing in different ways. Conflict equivalent : you need to say Schedule A is conflict equivalent to Schedule B. it must involve two

问题 There are many cases in which JavaScript's type-coercing equality operator is not transitive. For example, see "JavaScript equality transitivity is weird." However, are there any cases in which == isn't symmetric ? That is, where a == b is true and b == a is false ? 回答1: In Javascript, == is always symmetric. The spec says: NOTE 2 The equality operators maintain the following invariants: A != B is equivalent to !(A == B) . A == B is equivalent to B == A , except in the order of evaluation of

问题 There are many cases in which JavaScript's type-coercing equality operator is not transitive. For example, see "JavaScript equality transitivity is weird." However, are there any cases in which == isn't symmetric ? That is, where a == b is true and b == a is false ? 回答1: In Javascript, == is always symmetric. The spec says: NOTE 2 The equality operators maintain the following invariants: A != B is equivalent to !(A == B) . A == B is equivalent to B == A , except in the order of evaluation of

问题 I understand how equivalence testing works. How is it the same or different from boundary value testing? 回答1: Equivalence Class Testing EC Testing is when you have a number of test items (e.g. values) that you want to test but because of cost (time/money) you do not have time to test them all. Therefore you group the test item into class where all items in each class are suppose to behave exactly the same. The theory is that you only need to test one of each item to make sure the system works

问题 So I was asked this question today. Integer a = 3; Integer b = 2; Integer c = 5; Integer d = a + b; System.out.println(c == d); What will this program print out? It returns true. I answered it will always print out false because of how I understood auto (and auto un) boxing. I was under the impression that assigning Integer a = 3 will create a new Integer(3) so that an == will evaluate the reference rather then the primitive value. Can anyone explain this? 回答1: Boxed values between -128 to

问题 I just learned about the C++ construct called "placement new". It allows you to exactly control where a pointer points to in memory. It looks like this: #include <new> // Must #include this to use "placement new" #include "Fred.h" // Declaration of class Fred void someCode() { char memory[sizeof(Fred)]; void* place = memory; Fred* f = new(place) Fred(); // Create a pointer to a Fred(), // stored at "place" // The pointers f and place will be equal ... } (example from C++ FAQ Lite) In this

问题 I've been reading Douglas Crockford's JavaScript: The Good Parts, and I came across this weird example that doesn't make sense to me: '' == '0' // false 0 == '' // true 0 == '0' // true false == undefined // false false == null // false null == undefined // true The author also goes on to mention "to never use == and != . Instead, always use === and !== ". However, he doesn't explain why the above behavior is exhibited? So my question is, why are the above results as they are? Isn't

问题 This is an example: I have four time periods labeled as t=0, t=1, t=2, t=3. Each time has a value associated with it as shown below: the format of the text file is as follows: 0,213 1,-999 2,456 3,-1100 Basically, each of the value is in one period. What I want to do is to use those values and get all the values to t=0. If I draw a timeline, then I would have two values on the positive at t=0 and t=2, and two values on the negative at t=1 and t=3. Now, I want to go from the right hand side of

问题 If you google for PowerShell Eqv you currently will find the VBScript-to-Windows PowerShell Conversion Guide on top of the list. Yet the answer is much of technical help: Eqv Operator Definition: Performs a logical equivalence on two expressions. No doubt Eqv has its uses; we’re just not sure if it has any practical uses. Although there might be a Windows PowerShell equivalent we have to be honest: we didn’t look real hard for one. In fact, I used the Eqv operator (also written as: A↔B ) a

问题 Is it possible to test IP addresses for equivalence in a dual stack environment using both IPv4 and IPv6? If so, how? My application uses websocket++ on top of Boost ASIO. As an example, on my LAN, one application connects to another listening on 192.168.1.2 , but using this answer's IP address getter std::string s = socket.remote_endpoint().address().to_string(); gives ::ffff:192.168.1.3 as the client's address. The problem is that .2 will have its own node list with the original v4 address