Visual Basic .NET Language => 단락 연산자 (AndAlso

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result = expression1 그리고 또한 expression2
결과 = 표현식 1Elese 식 2

매개 변수

매개 변수	세부
결과	필수 사항. 부울 식입니다. 결과는 두 표현식을 비교 한 부울 결과입니다.
표현 1	필수 사항. 부울 식입니다.
표현 2	필수 사항. 부울 식입니다.

비고

'AndAlso' 와 'OrElse' 는 ShortCircuiting 연산자로, 컴파일러가 첫 번째 결과가 부울 비교의 부울 비교에있는 모든 표현식을 평가하지 않기 때문에 실행이 짧음을 의미합니다.

또한 용도

' Sometimes we don't need to evaluate all the conditions in an if statement's boolean check.

' Let's suppose we have a list of strings:

Dim MyCollection as List(Of String) = New List(of String)()

' We want to evaluate the first value inside our list:

If MyCollection.Count > 0 And MyCollection(0).Equals("Somevalue")
    Console.WriteLine("Yes, I've found Somevalue in the collection!")
End If 

' If MyCollection is empty, an exception will be thrown at runtime.
' This because it evaluates both first and second condition of the 
' if statement regardless of the outcome of the first condition.

' Now let's apply the AndAlso operator

If MyCollection.Count > 0 AndAlso MyCollection(0).Equals("Somevalue")
    Console.WriteLine("Yes, I've found Somevalue in the collection!")
End If 

' This won't throw any exception because the compiler evaluates just the first condition.
' If the first condition returns False, the second expression isn't evaluated at all.

기타 사용법

' The OrElse operator is the homologous of AndAlso. It lets us perform a boolean 
' comparison evaluating the second condition only if the first one is False

If testFunction(5) = True OrElse otherFunction(4) = True Then
    ' If testFunction(5) is True, otherFunction(4) is not called.
    ' Insert code to be executed.
End If

NullReferenceException 피하기

7.0

OrElse

Sub Main()
    Dim elements As List(Of Integer) = Nothing

    Dim average As Double = AverageElementsOrElse(elements)
    Console.WriteLine(average) ' Writes 0 to Console

    Try
        'Throws ArgumentNullException
        average = AverageElementsOr(elements)
    Catch ex As ArgumentNullException
        Console.WriteLine(ex.Message)
    End Try
End Sub

Public Function AverageElementsOrElse(ByVal elements As IEnumerable(Of Integer)) As Double
    ' elements.Count is not called if elements is Nothing so it cannot crash
    If (elements Is Nothing OrElse elements.Count = 0) Then
        Return 0
    Else
        Return elements.Average()
    End If
End Function

Public Function AverageElementsOr(ByVal elements As IEnumerable(Of Integer)) As Double
    ' elements.Count is always called so it can crash if elements is Nothing
    If (elements Is Nothing Or elements.Count = 0) Then
        Return 0
    Else
        Return elements.Average()
    End If
End Function

7.0

그리고 또한

Sub Main()
    Dim elements As List(Of Integer) = Nothing

    Dim average As Double = AverageElementsAndAlso(elements)
    Console.WriteLine(average) ' Writes 0 to Console

    Try
        'Throws ArgumentNullException
        average = AverageElementsAnd(elements)
    Catch ex As ArgumentNullException
        Console.WriteLine(ex.Message)
    End Try
End Sub

Public Function AverageElementsAndAlso(ByVal elements As IEnumerable(Of Integer)) As Double
    ' elements.Count is not called if elements is Nothing so it cannot crash
    If (Not elements Is Nothing AndAlso elements.Count > 0) Then
        Return elements.Average()
    Else
        Return 0
    End If
End Function

Public Function AverageElementsAnd(ByVal elements As IEnumerable(Of Integer)) As Double
    ' elements.Count is always called so it can crash if elements is Nothing
    If (Not elements Is Nothing And elements.Count > 0) Then
        Return elements.Average()
    Else
        Return 0
    End If
End Function

14.0

Visual Basic 14.0은 null 조건부 연산자를 도입 하여 예제의 AndAlso 버전의 동작을 모방 한 더 명확한 방식으로 함수를 다시 작성할 수 있습니다.

Modified text is an extract of the original Stack Overflow Documentation

아래 라이선스 CC BY-SA 3.0

와 제휴하지 않음 Stack Overflow

Visual Basic .NET Language
단락 연산자 (AndAlso - OrElse)

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