short-circuiting

问题 This question already has answers here : AndAlso/OrElse in VBA (7 answers) Closed 5 years ago . VBA doesn\'t short-circuit VBA does not support short-circuiting - apparently because it only has bitwise And/Or/Not etc operations. From the VBA language specification: \"Logical operators are simple data operators that perform bitwise computations on their operands.\" In this light, it makes sense that VBA was designed with true = &H1111 and false = &H0000 : this way logical statements can be

问题 Which of these subroutines is not like the other? sub or1 { my ($a,$b) = @_; return $a || $b; } sub or2 { my ($a,$b) = @_; $a || $b; } sub or3 { my ($a,$b) = @_; return $a or $b; } sub or4 { my ($a,$b) = @_; $a or $b; } I came to Perl 5 from C and Perl 4 and always used || until I saw more scripts using or and I liked the way it looked. But as the above quiz shows, it\'s not without its pitfalls for the unwary. For people who use both constructs or who use a lot of or , what rules of thumb do

问题 I want to consult SQL Server OR short-circuit Code: DECLARE @tempTable table ( id int ) INSERT @tempTable(id) values(1) DECLARE @id varchar(10) SET @id = \'x\' SELECT * FROM @tempTable WHERE 1=1 OR id = @id --successfully SELECT * FROM @tempTable WHERE @id = \'x\' OR id = @id --Exception not Convert \'x\' to int Why? 1=1 and @id=\'x\' is true. SQL Server OR operator : whether the short-circuit function？ THANKS 回答1: Within SQL, there is no requirement that an OR clause breaks early. In other

问题 I saw this line in the jQuery.form.js source code: g && $.event.trigger(\"ajaxComplete\", [xhr, s]); My first thought was wtf?? My next thought was, I can\'t decide if that\'s ugly or elegant. I\'m not a Javascript guru by any means so my question is 2-fold. First I want to confirm I understand it properly. Is the above line equivalent to: if (g) { $.event.trigger(\"ajaxComplete\", [xhr, s]); } And secondly is this common / accepted practice in Javascript? On the one hand it\'s succinct, but

问题 What is the difference between the & and && logical operators in MATLAB? 回答1: The single ampersand & is the logical AND operator. The double ampersand && is again a logical AND operator that employs short-circuiting behaviour. Short-circuiting just means the second operand (right hand side) is evaluated only when the result is not fully determined by the first operand (left hand side) A & B (A and B are evaluated) A && B (B is only evaluated if A is true) 回答2: && and || take scalar inputs and

问题 Given the following code: if (is_valid($string) && up_to_length($string) && file_exists($file)) { ...... } If is_valid($string) returns false , does the php interpreter still check later conditions, like up_to_length($string) ? If so, then why does it do extra work when it doesn\'t have to? 回答1: Yes, the PHP interpreter is "lazy", meaning it will do the minimum number of comparisons possible to evaluate conditions. If you want to verify that, try this: function saySomething() { echo 'hi!';

问题 In VB.NET, what is the difference between And and AndAlso ? Which should I use? 回答1: The And operator evaluates both sides, where AndAlso evaluates the right side if and only if the left side is true. An example: If mystring IsNot Nothing And mystring.Contains("Foo") Then ' bla bla End If The above throws an exception if mystring = Nothing If mystring IsNot Nothing AndAlso mystring.Contains("Foo") Then ' bla bla End If This one does not throw an exception. So if you come from the C# world,

问题 This question already has answers here : Is short-circuiting logical operators mandated? And evaluation order? (7 answers) Closed last year . When encountering a (bool1 && bool2), does c++ ever attempts to check bool2 if bool1 was found false or does it ignore it the way PHP does? Sorry if it is too basic of a question, but I really could not find a mentioning of that neither in Schildt nor on the Internet. 回答1: Yes, the && operator in C++ uses short-circuit evaluation so that if bool1

问题 In Perl (and other languages) a conditional ternary operator can be expressed like this: my $foo = $bar == $buz ? $cat : $dog; Is there a similar operator in VB.NET? 回答1: Depends upon the version. The If operator in VB.NET 2008 is a ternary operator (as well as a null coalescence operator). This was just introduced, prior to 2008 this was not available. Here's some more info: Visual Basic If announcement Example: Dim foo as String = If(bar = buz, cat, dog) [EDIT] Prior to 2008 it was "IIf",

问题 Does Python support short-circuiting in boolean expressions? 回答1: Yep, both and and or operators short-circuit -- see the docs. 回答2: Short-circuiting behavior in operator and , or : Let's first define a useful function to determine if something is executed or not. A simple function that accepts an argument, prints a message and returns the input, unchanged. >>> def fun(i): ... print "executed" ... return i ... One can observe the Python's short-circuiting behavior of and , or operators in the