The C# specification guarantees that both sides are evaluated exactly once from left-to-right and that no short-circuiting occurs. 5.3.3.21 General rules for expressions with embedded expressions The following rules apply to these kinds of expressions: parenthesized expressions (§7.6.3), element access expressions (§7.6.6), base access expressions with indexing (§7.6.8), increment and decrement expressions (§7.6.9, §7.7.5), cast … Read more
Depending on what exactly you need: is null checks whether the value is null: {% if var is null %} {# do something #} {% endif %} is defined checks whether the variable is defined: {% if var is not defined %} {# do something #} {% endif %} Additionally the is sameas test, which … Read more
Due to the low precedence of the ‘or’ operator, or3 parses as follows: sub or3 { my ($a,$b) = @_; (return $a) or $b; } The usual advice is to only use the ‘or’ operator for control flow: @info = stat($file) or die; For more discussion, see the perl manual: http://perldoc.perl.org/perlop.html#Logical-or-and-Exclusive-Or
All design processes result in compromises between mutually incompatible goals. Unfortunately, the design process for the overloaded && operator in C++ produced a confusing end result: that the very feature you want from && — its short-circuiting behavior — is omitted. The details of how that design process ended up in this unfortunate place, those … Read more
No, the B==2 part is not evaluated. This is called short-circuit evaluation. Edit: As Robert C. Cartaino rightly points out, if the logical operator is overloaded, short-circuit evaluation does not take place (that having been said, why someone would overload a logical operator is beyond me).
As a more general apprach, I suggest to introduce condition flags and make usage of assigning comparison results to booleans: dim cond1 as boolean dim cond2 as boolean cond1 = false cond2 = false ‘ Step 1 cond1 = MyObj Is Nothing ‘ Step 2: do it only if step 1 was sucessful if cond1 … Read more
Within SQL, there is no requirement that an OR clause breaks early. In other words, it is up to the optimizer whether to check both conditions simutaneously. I am not an expert in the MSSQL optimizer, but I have seen instances where the optimizer has and has not short circuited an OR clause.
Yes. In C# && and || are short-circuiting and thus evaluates the right side only if the left side doesn’t already determine the result. The operators & and | on the other hand don’t short-circuit and always evaluate both sides. The spec says: The && and || operators are called the conditional logical operators. They … Read more
Yes, it short-circuits: >>> def test(): … yield True … print(‘one’) … yield False … print(‘two’) … yield True … print(‘three’) … >>> all(test()) one False From the docs: Return True if all elements of the iterable are true (or if the iterable is empty). Equivalent to: def all(iterable): for element in iterable: if not … Read more
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 … Read more