MSDN Magazine - October 2007 - (Page 33)

expression can be passed,declaring parameters and the expression to return. In the following example, a function is declared that accepts a Customer and a String and returns a Boolean representing whether or not the Customer’s city matches the String.That function is then passed as a delegate to the Filter method, presumably to ﬁlter based on this Boolean value: Orders.Filter( _ Function(cust As Customer, city As String) cust.City = city) Since this is basically a function deﬁnition without a return type, it becomes clear how type inference can be useful in determining the expression’s type to declare the proper delegate and verify that type is valid. assigning some expression to an identiﬁer not deﬁned in the current scope.The result was that a variable of type Object was created and assigned the value speciﬁed, much as if this assignment was made in code with Option Explicit Off. In Visual Basic 2008, the behavior I described for the Immediate Window and the behavior I described with Option Explicit Off will be the same as they were with Visual Basic 2005, thus type inference will not take place. If I enter the following two commands into the Immediate Window, the following result will be displayed, showing an A Lambda expression Object variable given the allows the use of delegates Integer value 12: intVar = 12 ?intVar 12 {Integer} Other Implications When Option Explicit is turned off,a local variable can be used in code without an explicit declaration.As with the case described previously,the variable is assumed to be of type Object and all calls are late-bound. It is worth noting that type inference does not occur on implicitly deﬁned variables,so the behavior has not changed at all. The following code shows an example: Sub SwapTwoInts(ByVal x As Integer, ByVal y As Integer) z=x x=y y=z End Sub Go To Type Deﬁnition When types are explicitly given in a variable deﬁnition, the Visual Studio® “Go To Deﬁnition” action can easily be invoked from the context menu of the type identiﬁer to determine where the type is deﬁned. In the following case, the user can click on IEnumerable and the result will be IEnumerable(Of T) in the Object Browser: Dim customers As IEnumerable(Of Customer) = GetCustomers() for simple functions in an inline fashion. This is useful for passing simple delegates as parameters. Using Visual Basic 2005, it was possible to declare a temporary variable implicitly in the Immediate Window while debugging by With the new language features discussed here, I expect that http://gate.com http://gate.com/msdn

Table of Contents Feed for the Digital Edition of MSDN Magazine - October 2007

Cover Contents Toolbox CLR Inside Out Basic Instincts Data Points Cutting Edge Pooled Threads WPF Threads Parallel Linq Parallel Performance Mobile Apps Test Run Foundations Windows with C++ Netting C++ .NET Matters { End Bracket } Net Nuptials

MSDN Magazine - October 2007

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