short-circuiting

问题 Related Questions : Benefits of using short-circuit evaluation, Why would a language NOT use Short-circuit evaluation?, Can someone explain this line of code please? (Logic & Assignment operators) There are questions about the benefits of a language using short-circuit code, but I'm wondering what are the benefits for a programmer? Is it just that it can make code a little more concise? Or are there performance reasons? I'm not asking about situations where two entities need to be evaluated

问题 Consider this code snippet, template<bool b> struct other { static const bool value = !b; }; template<bool b> struct test { static const bool value = b || other<b>::value; }; int main() { bool value = test<true>::value; } Do compilers instantiate other<true> in situations such as the above, when instantiating seems completely unnecessary? Or just because I've written the syntax other<b>::value , compilers must instantiate it regardless of the fact that it contributes absolutely nothing to the

问题 Consider this code snippet, template<bool b> struct other { static const bool value = !b; }; template<bool b> struct test { static const bool value = b || other<b>::value; }; int main() { bool value = test<true>::value; } Do compilers instantiate other<true> in situations such as the above, when instantiating seems completely unnecessary? Or just because I've written the syntax other<b>::value , compilers must instantiate it regardless of the fact that it contributes absolutely nothing to the

问题 I've got a query that I've just found in the database that is failing causing a report to fall over. The basic gist of the query: Select * From table Where IsNull(myField, '') <> '' And IsNumeric(myField) = 1 And Convert(int, myField) Between @StartRange And @EndRange Now, myField doesn't contain numeric data in all the rows [it is of nvarchar type]... but this query was obviously designed such that it only cares about rows where the data in this field is numeric. The problem with this is

问题 All this time my thinking of short circuit evaluations seems to be wrong. In javascript: var a = false, b = true, c=true; a && b || c; // Evaluates to true Compared to var a = false, b = true, c=true; a && (b || c); // Evaluates to true Why doesn't the VM stop when it sees that a is false? More explicit example: function a(){ console.log("I'm A"); return false; } function b(){ console.log("I'm B"); return true; } function c(){ console.log("I'm C"); return true; } a() && b() || c(); The output

问题 All this time my thinking of short circuit evaluations seems to be wrong. In javascript: var a = false, b = true, c=true; a && b || c; // Evaluates to true Compared to var a = false, b = true, c=true; a && (b || c); // Evaluates to true Why doesn't the VM stop when it sees that a is false? More explicit example: function a(){ console.log("I'm A"); return false; } function b(){ console.log("I'm B"); return true; } function c(){ console.log("I'm C"); return true; } a() && b() || c(); The output

问题 I'm a Python developer and I just started learning Rails, so this might be a noobish question. I found some surprising behavior in my code: <!-- render flash message array if set --> <% if flash[:notice].is_a? Array && !flash[:notice].empty? %> This results in the following error: undefined method `empty?' for nil:NilClass It seems like Ruby should not be calling .empty? in the second part of this clause. I confirmed that short-circuit evaluation works in other cases: # this is more what I

问题 Consider this code Object found = collection.stream() .filter( s -> myPredicate1(s)) .filter( s -> myPredicate2(s)) .findAny() Will it process entire stream, and call both myPredicate1 and myPredicate2 for all elements of the collection? Or will as many predicates be called as are needed to actually find the value? 回答1: Yes it is, as the Stream.findAny() documentation states: This is a short-circuiting terminal operation. It's a common misconception that objects in stream are "pushed" towards

问题 #include <type_traits> #define FORWARD(arg)\ std::forward<decltype(arg)>(arg) template<typename... Args> constexpr bool AndL(Args&&... args) { return (... && FORWARD(args)); } template<typename... Args> constexpr bool AndR(Args&&... args) { return (FORWARD(args) && ...); } int main() { bool* pb = nullptr; false && (*pb = true); // ok at runtime. AndL(false, (*pb = true)); // error at runtime! AndR(false, (*pb = true)); // error at runtime! } The traditional && operator supports short-circuit

问题 #include <type_traits> #define FORWARD(arg)\ std::forward<decltype(arg)>(arg) template<typename... Args> constexpr bool AndL(Args&&... args) { return (... && FORWARD(args)); } template<typename... Args> constexpr bool AndR(Args&&... args) { return (FORWARD(args) && ...); } int main() { bool* pb = nullptr; false && (*pb = true); // ok at runtime. AndL(false, (*pb = true)); // error at runtime! AndR(false, (*pb = true)); // error at runtime! } The traditional && operator supports short-circuit