Instrução Function (Visual Basic)

Declares the name, parameters, and code that define a Function procedure.

Observação
Visual Basic 2008apresenta as expressões lambda, que permitem que você definir expressões de função na linha. For more information, see Expressão de função (Visual Basic) and Expressões Lambda (Visual Basic).

[ <attributelist> ] [ accessmodifier ] [ proceduremodifiers ] [ Shared ] [ Shadows ] 
Function name [ (Of typeparamlist) ] [ (parameterlist) ] [ As returntype ] [ Implements implementslist | Handles eventlist ]
    [ statements ]
    [ Exit Function ]
    [ statements ]
End Function

Parts

Comentários

All executable code must be inside a procedure. Each procedure in turn is declared within a class, structure, or module, which is called the containing class, structure, or module.

Use a Function procedure when you need to return a value to the calling code. Use a Sub procedure when you do not need to return a value.

Você pode definir um Function procedimento somente no nível de módulo . This means the declaration context for a function must be a class, structure, module, or interface, and cannot be a source file, namespace, procedure, or block. For more information, see Contextos de declaração e níveis de acesso padrão (Visual Basic).

Function procedures default to public access. You can adjust their access levels with the access modifiers.

Você pode chamar um Function procedimento no lado direito de uma expressão quando desejar usar o valor retornado pela função. You use the Function procedure the same way you use any library function such as Sqrt, Cos, or ChrW.

You call a Function procedure by using the procedure name, followed by the argument list in parentheses, in an expression. You can omit the parentheses only if you are not supplying any arguments. However, your code is more readable if you always include the parentheses.

A function can also be called using the Call statement, in which case the return value is ignored.

Rules

• Return Type. O Functiondedemonstrativo pode declarar o tipo de dados de que o valor retornado. You can specify any data type or the name of an enumeration, structure, class, or interface.

  If you do not specify returntype, the procedure returns Object.

• Implementação. Se este procedimento usa o Implementspalavra-chave, o que contém uma classe ou estrutura também deve ter um Implementsademonstrativo imediatamente seguinte sua Class ou Structuredemonstrativo. The Implements statement must include each interface specified in implementslist. However, the name by which an interface defines the Function (in definedname) does not have to be the same as the name of this procedure (in name).

Behavior

• Returning from a Procedure. Quando o Function procedimento retorna para o código de chamada, a execução continua com a demonstrativo após a demonstrativo que chamou.

  The Exit Function and Return statements cause an immediate exit from a Function procedure. Any number of Exit Function and Return statements can appear anywhere in the procedure, and you can mix Exit Function and Return statements.

• Valorde retorno. Para retornar um valor de uma função, você pode atribuir o valor ao nome da função ou incluí-lo em um Return demonstrativo. The following example assigns the return value to the function name myFunction and then uses the Exit Function statement to return.

  Function myFunction(ByVal j As Integer) As Double
      myFunction = 3.87 * j
      Exit Function
  End Function
  

  If you use Exit Function without assigning a value to name, the procedure returns the default value for the data type specified in returntype. If returntype is not specified, the procedure returns Nothing, the default value for Object.

  The Return statement simultaneously assigns the return value and exits the function. The following example shows this.

  Function myFunction(ByVal j As Integer) As Double
      Return 3.87 * j
  End Function
  

Troubleshooting

• Order of Execution. Visual Basic sometimes rearranges arithmetic expressions to increase internal efficiency. For that reason, avoid using a Function procedure in an arithmetic expression when the function changes the value of variables in the same expression.

Exemplo

The following example uses the Function statement to declare the name, parameters, and code that form the body of a Function procedure. The ParamArray modifier enables the function to accept a variable number of arguments.

Public Function calcSum(ByVal ParamArray args() As Double) As Double
    calcSum = 0
    If args.Length <= 0 Then Exit Function
    For i As Integer = 0 To UBound(args, 1)
        calcSum += args(i)
    Next i
End Function

The following example invokes the function declared in the preceding example.

Module Module1

    Sub Main()
        ' In the following function call, calcSum's local variables 
        ' are assigned the following values: args(0) = 4, args(1) = 3, 
        ' and so on. The displayed sum is 10.
        Dim returnedValue As Double = calcSum(4, 3, 2, 1)
        Console.WriteLine("Sum: " & returnedValue)
        ' Parameter args accepts zero or more arguments. The sum 
        ' displayed by the following statements is 0.
        returnedValue = calcSum()
        Console.WriteLine("Sum: " & returnedValue)
    End Sub

    Public Function calcSum(ByVal ParamArray args() As Double) As Double
        calcSum = 0
        If args.Length <= 0 Then Exit Function
        For i As Integer = 0 To UBound(args, 1)
            calcSum += args(i)
        Next i
    End Function

End Module

Consulte também

Tarefas

Como: Usar uma classe genérica (Visual Basic)

Solucionando problemas de procedimentos (Visual Basic)

Referência

Instrução Sub (Visual Basic)

Lista de parâmetros (Visual Basic)

Instrução Dim (Visual Basic)

Instrução Call (Visual Basic)

Cláusula Of (Visual Basic)

Expressão de função (Visual Basic)

Conceitos

Matrizes de parâmetros (Visual Basic)

Expressões Lambda (Visual Basic)