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I have always used || (two pipes) in OR expressions, both in C# and PHP. Occasionally I see a single pipe used: |. What is the difference between those two usages? Are there any caveats when using one over the other or are they interchangeable?
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The | operator evaluates both operands even if the left-hand operand evaluates to true, so that the operation result is true regardless of the value of the right-hand operand. The conditional logical OR operator ||, also known as the "short−circuiting" logical OR operator, computes the logical OR of its operands.
The logical OR operator ( || ) returns the boolean value true if either or both operands is true and returns false otherwise.
&& is used to perform and operation means if anyone of the expression/condition evaluates to false whole thing is false. || is used to perform or operation if anyone of the expression/condition evaluates to true whole thing becomes true.
In short, the difference between the two operators boils down to the difference between falsy and null/undefined . Where the logical or ( || ) operator takes the right operand in the case of a falsy value — which includes empty string, 0, false, NaN, etc.
Just like the & and && operator, the double Operator is a "short-circuit" operator.
For example:
if(condition1 || condition2 || condition3) If condition1 is true, condition 2 and 3 will NOT be checked.
if(condition1 | condition2 | condition3) This will check conditions 2 and 3, even if 1 is already true. As your conditions can be quite expensive functions, you can get a good performance boost by using them.
There is one big caveat, NullReferences or similar problems. For example:
if(class != null && class.someVar < 20) If class is null, the if-statement will stop after class != null is false. If you only use &, it will try to check class.someVar and you get a nice NullReferenceException. With the Or-Operator that may not be that much of a trap as it's unlikely that you trigger something bad, but it's something to keep in mind.
No one ever uses the single & or | operators though, unless you have a design where each condition is a function that HAS to be executed. Sounds like a design smell, but sometimes (rarely) it's a clean way to do stuff. The & operator does "run these 3 functions, and if one of them returns false, execute the else block", while the | does "only run the else block if none return false" - can be useful, but as said, often it's a design smell.
There is a Second use of the | and & operator though: Bitwise Operations.
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