How is OR handled?

General
1

If you have a statement in code like:

If X = true OR Y = true then…

If X = true, does it still evaluate to see if Y is true or does it skip the evaluation as being redundant?

2

if X is true it skips testing Y.

Btw, you can also write this as: if X or Y then

3

Also, there’s a similar situation with AND.

[code]dim f As Folderitem = getMyFile

if f <> nil and f.Exists then
//process
end[/code]

If f is nil it doesn’t test f.Exists.

4

Perfect. That explains what I was seeing. Thanks!

5

And it’s something that bites a lot of VB6 converts because in VB6 it evaluates the entire line. I like the Xojo way much better.

6

Xojo is much more like how most modern compiler treat boolean expression evaluation for AND / OR etc

IF condition1 or condition2 (and how ever many more you want)

need NOT evaluate condition2 and any others if condition1 is true since it wont matter what they return - the OR will be true

the same is true for AND

IF condition1 AND condition2 (and how ever many more you want)

need not evaluate condition2 etc if condition1 is FALSE because it wont matter

   OR   true   false           AND      true    false
 true   true   true           true      true    false
false   true   false         false      false   false
7

I had no idea (or perhaps just forgot) that other languages did this differently. This seems only logical.

8

Allmost all languages have bitwise logic functions/operators and boolean logic (mostly short-circuiting) function/operators. & vs && in C++, C#, Java. In VB .NET And and Or are non-short-circuiting. Why? Because they do not only work on two booleans, but also on two integers. So MS introduced AndAlso and OrElse. Historically bitwise logic is of course older (Machine Language, Assembly) than boolean logic (ALGOL and its descendants).