OrElse operator
Performs a short-circuit logical disjunction of two Boolean expressions. If the left operand evaluates to True, the right operand is not evaluated.
Note
OrElse is a twinBASIC extension. The classic Or operator always evaluates both operands and returns a bitwise result; OrElse evaluates the right operand only when needed and always returns a Boolean.
Syntax:
result = expression1 OrElse expression2
- result
- A Boolean variable.
- expression1, expression2
- Any expressions that evaluate to Boolean (or are coercible to Boolean).
If expression1 is True, result is True and expression2 is not evaluated. Otherwise expression2 is evaluated and its Boolean value becomes result.
This is the standard “short-circuit OR”. It is useful when expression2 is more expensive to evaluate, or when expression2 would fail or have unwanted side effects in the case where expression1 is already True.
Example
Skipping an expensive lookup when a cheaper test already proves the condition:
If IsCached(key) OrElse FetchFromDisk(key) Then
' FetchFromDisk is only called when IsCached returned False.
Process key
End If
Compare with the equivalent code using Or, which would always call FetchFromDisk even when the cached lookup already succeeded:
' Inefficient - FetchFromDisk runs even when IsCached returned True.
If IsCached(key) Or FetchFromDisk(key) Then
Process key
End If