short-circuiting

问题 In other words, do the following two statements behave the same way? isFoobared = isFoobared && methodWithSideEffects(); isFoobared &= methodWithSideEffects(); I realize I could just write up a test, but someone might know this offhand, and others might find the answer useful. 回答1: No, |= and &= do not shortcircuit, because they are the compound assignment version of & and | , which do not shortcircuit. JLS 15.26.2 Compound Assignment Operators A compound assignment expression of the form E1

问题 If I write two SELECT statements in a IF EXISTS condition with a AND clause in between these select queries, does both queries get executed even if the first SELECT returns false? IF EXISTS (SELECT....) AND EXISTS(SELECT ....) BEGIN END Does the SQL Server Engine execute both the SQL Statement in this scenario? Thanks Krish 回答1: I would rewrite the test as IF CASE WHEN EXISTS (SELECT ...) THEN CASE WHEN EXISTS (SELECT ...) THEN 1 END END = 1 This guarantees short circuiting as described here

问题 I want to be able to evaluate whether a function accepts one argument of type int, and whether it returns void. To that end I used std::conjunction since I believed it was supposed to short-circuit and not evaluate the second ill-formed expression in case the function is not callable with one argument of type int, but for some reason I get a compiler error: #include <iostream> #include <type_traits> template<typename Function> struct oneArgVoid { static constexpr bool value = std::conjunction

问题 Oracle defines several structures that make use of what looks like lazy evaluation but what's actually short-circuiting. For example: x := case when 1 = 2 then count_all_prime_numbers_below(100000000) else 2*2 end; The function count_all(...) will never be called. However, what I'm more interested in is the syntax that looks like regular function call: x := coalesce(null, 42, hundreth_digit_of_pi()); Hundreth_digit_of_pi() will not be called since coalesce is not a regular function, but a

问题 I want to write a templatized function which takes either an array<int, 3> or an int[3] . I'm trying to capture that in an enable_if : template<typename T> enable_if_t<is_array_v<T> && extent_v<T> == 3U || !is_array_v<T> && tuple_size<T>::value == 3U> foo(const T& param) {} Unfortunately for an int[3] , tupple_size is not defined, which causes the template to fail to compile, before short circuiting is evaluated. I have also tried to do this using a conditional but that has the same problem

问题 If I have the following ... a OrElse b ... and a is True then clearly b is never evaluated. But if I add an Or , then what? a OrElse b Or c Does/should c get evaluated? And what if I put in some brackets? Apologies if this is basic. Of course I can test for the answer myself but I can't find this question answered here or elsewhere. Lots of questions dealing with Or versus OrElse but nothing dealing with Or with OrElse 回答1: This is an operator precedence problem. The relevant documentation is

问题 Given a container of boolean values (An example is std::vector<bool> ), is there a standard function that returns true if all the values are true ("and") or true if at least one value is true ("or"), with short circuit evalutation ? I digged trough www.cplusplus.com this morning but couldn't find anything close. 回答1: You can implement by: AND: std::find(vector.begin(), vector.end(), false) == vector.end() // all the values are true OR: std::find(vector.begin(), vector.end(), true) != vector

问题 Are there any short-circuit logic operators (specifically short-circuit AND and short-circuit OR ) that I can use in a WHERE clause in MySQL 5.5? If there isn't, what are the alternatives? An abstract view at my problem along with an explanation as to why I need this can be found at this fiddle: http://sqlfiddle.com/#!2/97fd1/3 In reality we are looking at millions of books in millions of bookstores in thousands of cities in hundreds of countries, which is why we cannot accept the overhead of

问题 I'm aware of Swift's higher-order functions like Map, Filter, Reduce and FlatMap, but I'm not aware of any like 'All' or 'Any' which return a boolean that short-circuit on a positive test while enumerating the results. For instance, consider you having a collection of 10,000 objects, each with a property called isFulfilled and you want to see if any in that collection have isFulfilled set to false. In C#, you could use myObjects.Any(obj -> !obj.isFulfilled) and when that condition was hit, it

问题 Let's say I have a simple function like this: int all_true(int* bools, int len) { if (len < 1) return TRUE; return *bools && all_true(bools+1, len-1); } This function can be rewritten in a more obviously tail-recursive style as follows: int all_true(int* bools, int len) { if (len < 1) return TRUE; if (!*bools) return FALSE; return all_true(bools+1, len-1); } Logically, there is zero difference between the two; assuming bools contains only TRUE or FALSE (sensibly defined), they do exactly the