Question

If I have the following …

a OrElse b 

… and a is True then clearly b is never evaluated. But if I add an Or, then what?

a OrElse b Or c

Does/should c get evaluated? And what if I put in some brackets?

Apologies if this is basic. Of course I can test for the answer myself but I can’t find this question answered here or elsewhere. Lots of questions dealing with Or versus OrElse but nothing dealing with Or with OrElse

Answer 1

This is an operator precedence problem. The relevant documentation is here:
http://msdn.microsoft.com/en-us/library/fw84t893.aspx?ppud=4

The important excerpts:

• Operators with equal precedence are evaluated left to right in the order in which they appear in the expression.

and

Inclusive disjunction (Or, OrElse)

So what we learn here is that Or and OrElse have the same precedence and that operators with the same precedence are evaluated from left to right.

Therefore, I would expect that in cases where a is true, b is not evaluated. However, c still will be. In cases where a is false, b is evaluated and regardless of the b‘s value the Or operator will evaluate c. So, yes, c is always evaluated.

As a practical matter, you should generally prefer OrElse in your code unless you have a good reason to use Or. Or exists now mainly for backwards compatibility.