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.
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
Closest thing I can find to an ‘official’ mention of PHP’s short-circuit implementation: http://php.net/manual/en/language.operators.logical.php
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
Since you wanted the spec, here it is (from §15.25 Conditional Operator ? :, the last sentence of the section): The operand expression not chosen is not evaluated for that particular evaluation of the conditional expression.
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
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
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
Yes, your two examples are equivalent. It works like this in pretty much all languages, but it’s become rather idiomatic in Javascript. Personally I think it’s good in some situations but can be abused in others. It’s definitely shorter though, which can be important to minimize Javascript load times. Also see Can somebody explain how … Read more