Question

I want to use “*” or “\” as mathematical operators as such:

“I am going to clarify”

dim tbox as textbox
tbox.text = "*"

dim i as integer = 8 tbox.text 3

“End Clarify”

dim [mult] as string = "*"
dim [div] as string = "\"


dim i as integer = 8 [mult] 3

and the result would be i is equal to 24

or

dim i as integer = 8 [div] 2 

and the result would be i is equal to 4

Can anyone solve this in one line without building a long, complex function? I would also like for this to be something that is already a part of the VB.NET structure and doesn’t require an import.

If such a solution does not exist how do I do it with a function or .dll import?

Answer 1

Insert This into where you want to evaluate.

dim [mult] as string = "*"
dim [div] as string = "\"


'dim i as integer = 8 [mult] 3

op = mult

dim i As Integer = Eval("8" & op & "3")

'i is your result


  Private Function Eval(ByVal command As String) As Object
    Dim MyProvider As New VBCodeProvider 'Create a new VB Code Compiler
    Dim cp As New CodeDom.Compiler.CompilerParameters     'Create a new Compiler parameter object.

    cp.GenerateExecutable = False        'Don't create an object on disk
    cp.GenerateInMemory = True           'But do create one in memory.

    'If cp.OutputAssembly is used with a VBCodeProvider, it seems to want to read before it is executed. 

    'See C# CodeBank example for explanation of why it was used.



    'the below is an empty VB.NET Project with a function that simply returns the value of our command parameter.

    Dim ClassName As String = "class" & Now.Ticks

    Dim TempModuleSource As String = "Imports System" & Environment.NewLine & _
                                     "Namespace ns " & Environment.NewLine & _
                                     "    Public Class " & ClassName & Environment.NewLine & _
                                     "        Public Shared Function Evaluate()" & Environment.NewLine & _
                                     "            Return (" & command & ")" & Environment.NewLine & _
                                     "        End Function" & Environment.NewLine & _
                                     "    End Class" & Environment.NewLine & _
                                     "End Namespace"

    'Create a compiler output results object and compile the source code.

    Dim cr As CodeDom.Compiler.CompilerResults = MyProvider.CompileAssemblyFromSource(cp, TempModuleSource)

    If cr.Errors.Count > 0 Then

      'If the expression passed is invalid or "", the compiler will generate errors.

      'Throw New ArgumentOutOfRangeException("Invalid Expression - please use something VB could evaluate")
      Return Nothing
    Else

      'Find our Evaluate method.
      Dim methInfo As Reflection.MethodInfo = cr.CompiledAssembly.GetType("ns." & ClassName).GetMethod("Evaluate")

      'Invoke it on nothing, so that we can get the return value
      Return methInfo.Invoke(methInfo, New Object() {})
    End If
  End Function