VB.NET program that uses directives#Const SPECIAL = 1
' Local variable.
Dim a As Integer = 1
' Use special value is SPECIAL is 1.
#If SPECIAL = 1 Then
a = 2#End If
' Display value.
Region. Another directive available in VB.NET programs is #Region. This directive partitions a code file. It has no effect on the compiled program.
Info: We use #Region to organize code. In Visual Studio, a region can be collapsed and expanded.
Also: Regions are used by Visual Studio when auto-generation of code files is performed, as for Windows Forms.
Note: Regions in VB.NET cannot be used in all locations. They must enclose an entire Function body or other unit of code.
VB.NET program that uses Region
''' Initialize the program.
A discussion. Preprocessing directives are handled at an early stage of compilation. The preprocessor scans VB.NET programs before compiling code statements into intermediate language.
Info: Directives are separate from the rest of the VB.NET code. This gives them special abilities.
And: With preprocessing directives, no performance loss is incurred with branches of an #If. The branches are handled before execution.
Caution: One problem with preprocessing directives is bit rot. Code that is not compiled because of an #If may become buggy or invalid.
A summary. Directives add another layer of compilation to VB.NET programs. With #If, #Const and even #Region, we access another set of abilities in this language.