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Short-circuiting logical expressions

Introduction

In LotusScript, logical operations (And and Or) evaluate all expressions before deciding which branch of the conditional statement to process. VoltScript adds new operators - || and && - for short-circuiting the logical operations.

||

|| short-circuits logical expressions where developers might otherwise use Or. This performs like Visual Basic's OrElse operator, running the minimum conditional statements required. The following code won't throw an error and continue to the Return statement.`

Function orSuccess as String
    Dim obj as Student
    If (obj is Nothing || obj.Name != "") Then
        Print "Student not initialized"
    End If
    Return "Success"
End Function

Note

Because || can now be an empty string and OrElse, If passedStr = "" || args(0) = "" Then won't compile. The first condition will need to be wrapped in parentheses, so If (passesStr = "") || args(0) = "" Then.

&&

&& short-circuits logical conjunctions on two or more expressions. This performs like Visual Basic's AndAlso operator, running the minimum conditional statements required. The following code won't run the obj.Score condition if obj.Name is blank.

Function andSuccess as String
    Dim obj as New Student
    If (obj.Name != "" && obj.Score > 90) Then
        Print "High-score valid student"
    End If
    Return "Success"
End Function

Understanding when to short-circuit

There may still be cases when you do not want to short-circuit logical expressions. When running unit tests, you want to know if all are successful or any have failed. TestSuite.ranSuccessfully() returns whether that test was successful. But consider the following script:

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Sub Initialize

    Dim testRunner as New testRunner("Language tests")
    Dim result as Boolean

    result = errorTests(testRunner)
    result = result And logicalTests(testRunner)

    If result Then Print "TESTS SUCCESSFUL" Else Print "TESTS UNSUCCESSFUL"

End Sub

If you used && on line 7, the second set of tests would only run of the first tests failed. But you want to run them every time. As a result, And is the better choice for this use case.

The complete implementations of the code snippets are available on GitHub.