In Visual Basic .NET, block passing refers to the ability to pass a block of code as a parameter to a method or function. This can be useful in situations where you need to perform an operation on a large number of elements, but the specific operation may vary depending on the context.
Here is an example of how to use block passing in Visual Basic .NET:
' Define a delegate that represents a block of code that takes an integer parameter and returns a boolean value
Delegate Function Predicate(ByVal value As Integer) As Boolean
' Define a method that takes an array of integers and a Predicate delegate as parameters.
' The method will return a new array containing only the integers that satisfy the predicate condition.
Function Filter(ByVal values As Integer(), ByVal predicate As Predicate) As Integer()
Dim result As New List(Of Integer)
For Each value In values
If predicate(value) Then
result.Add(value)
End If
Next
Return result.ToArray()
End Function
' Define a few sample Predicate delegates that can be passed to the Filter method
Function IsEven(ByVal value As Integer) As Boolean
Return (value Mod 2 = 0)
End Function
Function IsPositive(ByVal value As Integer) As Boolean
Return (value > 0)
End Function
' Use the Filter method with the IsEven predicate
Dim numbers() As Integer = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
Dim evenNumbers() As Integer = Filter(numbers, AddressOf IsEven)
' Use the Filter method with the IsPositive predicate
Dim positiveNumbers() As Integer = Filter(numbers, AddressOf IsPositive)
In this example, we define a delegate type called Predicate that represents a block of code that takes an integer parameter and returns a boolean value. We then define a method called Filter that takes an array of integers and a Predicate delegate as parameters. The method iterates over each element in the input array and applies the predicate to determine whether it should be included in the output array.
Finally, we define a few sample predicate delegates (IsEven and IsPositive) and use them with the Filter method to extract different subsets of numbers from the original array. By passing a block of code (the predicate) as a parameter to the Filter method, we can reuse the same filtering logic in multiple contexts without having to rewrite the entire method each time.