short-circuiting

问题 I would like to know if JavaScript has "short-circuit" evaluation like && Operator in C#. If not, I would like to know if there is a workaround that makes sense to adopt. 回答1: Yes, JavaScript has "short-circuit" evaluation. if (true == true || foo.foo){ // Passes, no errors because foo isn't defined. } Live DEMO if (false && foo.foo){ // Passes, no errors because foo isn't defined. } Live DEMO 回答2: This answer goes into great detail on how short-circuiting works in JavaScript, with all the

问题 This is My Code: int main() { int i=2,j=2,c=2,d; d= ++i || ++j && c; printf("I is %d\n",i); printf("J is %d\n",j); printf("C is %d\n",c); printf("D is %d\n",d); return 0; } The output of the following code is: i is 3 j is 2 c is 2 d is 1 Now my question is, if ++i is 3 then why ++j is 2? What is the difference between ++i & i++ ? Also I want to know that how come d is 1 ? 回答1: You asked: Now my question is if ++i is 3 then why ++j is 2? ++j is never executed since ++i evaluates to true. The

问题 This is probably a rather simple question, but I'm at a loss... I have an if statement like the following: if(TheEnum.A.equals(myEnum) || TheEnum.B.equals(myEnum)) TheEnum can be A , B , C , ... G (more than just 4 options). JaCoCo (SONAR) tells me that there are four conditions I can cover here. Which ones are those? Isn't the entire set I can test for in this instance essentially if(true || not_evaluated) => true if(false || true) => true if(false || false) => false I'm pretty sure I can't

问题 In general, the short circuit or operator || ignores the right side of the or if the left side evaluates to true. Apparently, we've found an exception to this. Check out the following: if (foo == null || bar != true ? foo.Count == 0 : true) { } This code throws a null reference exception on the command foo.Count because foo is null. And naturally, the boolean logic allows for this. But, if foo is null you would expect that the or would short circuit and not even evaluate the right side of the

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 3 years ago . For instance (Lets say we are talking about C++ if that makes a differnce), In an && operator if I know that one statement will result to 0 more often/has a higher chance then the other statement should I put that on the left side, and the other statement on the right? Same

问题 I cannot produce example in Python which shows Boolean operator precedence rules combined with short circuit evaluation. I can show operator precedence using: print(1 or 0 and 0) # Returns 1 because `or` is evaluated 2nd. But the issue with short circuiting shows up when I change it to this: def yay(): print('yay'); return True def nay(): print('nay') def nope(): print('nope') print(yay() or nay() and nope()) # Prints "yay\nTrue" For each of 4 possibilities when expression before or is True

问题 We all know about short circuiting in logical expressions, i.e. when if ( False AND myFunc(a) ) then ... doesn't bother executing myFunc() because there's no way the if condition can be true. I was curious as to whether there is an equivalent for your everyday algebraic equation, say result = C*x/y + z If C=0 there is no point in evaluating the first term. It wouldn't matter much performance-wise if x and y were scalars, but if we pretend they are large matrices and the operations are costly

问题 Suppose I want to check a bunch of objects to make sure none is null: if (obj != null && obj.Parameters != null && obj.Parameters.UserSettings != null) { // do something with obj.Parameters.UserSettings } It is an alluring prospect to write a helper function to accept a variable number of arguments and simplify this kind of check: static bool NoNulls(params object[] objects) { for (int i = 0; i < objects.Length; i++) if (objects[i] == null) return false; return true; } Then the above code

问题 I'm learning the book named Data Structures & Algorithms in Python . On Page 12 that introduce the Logical Operators , it writes: The and and or operators short-circuit , (I thinks it should add is called ), in that they do not evaluate the second operand if the result can be determined based on the value of the first operand. This feature is useful when constructing Boolean expressions in which we first test that a certain condition holds (such as a reference not being None), and then test a

问题 In JavaScript and Java, the equals operator ( == or === ) has a higher precedence than the OR operator ( || ). Yet both languages (JS, Java) support short-circuiting in if statements: When we have if(true || anything()) , anything() isn't evaluated. You can also have the following expression: true || foo == getValue()) - for example in an output statement such as console.log(...); , or in an assignment. Now, according to operator precedence, short-circuiting shouldn't happen, as === = == > ||