For a while now I've been playing around with various ways of passing a logical predicate E.G. >= someValue as an argument to a function. (see: If ComparisonIsTrue(thisPost, ComparisonOperator.NotEqualTo, goodCode) Then Me.Answer and a global enum for comparison operators)

In the end, I've decided to build a CLS_Comparison_Predicate class with Operator and RightValue properties, with a Compare() function that takes a LeftValue as an argument.

Thoughts?

Example Usage:

Dim predicate As CLS_Comparison_Predicate
Set predicate = New CLS_Comparison_Predicate

predicate.Operator = GreaterThan
predicate.RightValue = 9000

If predicate.Compare(inputValue) Then
    MsgBox "It's over 9,000!"
End If

Enum:

Public Enum ComparisonOperator
    NotEqualTo = 0
    LessThan = 1
    LessThanOrEqualTo = 2
    EqualTo = 3
    GreaterThanOrEqualTo = 4
    GreaterThan = 5
End Enum

Code:

Option Explicit

Private pOperator As ComparisonOperator
Private pRightValue As Variant

Private Const NULL_ERROR_TEXT As String = "Invalid Compare input. Cannot compare against Null"
Private Const OBJECT_ERROR_TEXT As String = "Invalid compare input. Input must be a value, not an object"

Public Property Let Operator(ByVal inputOperator As ComparisonOperator)
    pOperator = inputOperator
End Property

Public Property Let RightValue(ByVal inputValue As Variant)
    If IsNull(inputValue) Then
        PrintErrorMessage NULL_ERROR_TEXT
        Stop
    ElseIf IsObject(inputValue) Then
        PrintErrorMessage OBJECT_ERROR_TEXT
        Stop
    End If

    pRightValue = inputValue
End Property

Public Function Compare(ByVal leftValue As Variant) As Boolean

    If IsNull(leftValue) Then
        PrintErrorMessage NULL_ERROR_TEXT
        Stop
    ElseIf IsObject(leftValue) Then
        PrintErrorMessage OBJECT_ERROR_TEXT
        Stop
    End If

    Dim isTrue As Boolean
    Select Case pOperator
        Case NotEqualTo
            isTrue = (leftValue <> pRightValue)
    
        Case LessThan
            isTrue = (leftValue < pRightValue)
        
        Case LessThanOrEqualTo
            isTrue = (leftValue <= pRightValue)
        
        Case EqualTo
            isTrue = (leftValue = pRightValue)
        
        Case GreaterThanOrEqualTo
            isTrue = (leftValue >= pRightValue)
        
        Case GreaterThan
            isTrue = (leftValue > pRightValue)
        
        Case Else
            '/ TODO: Error Handling
            Stop
    End Select
        
    Compare = isTrue

End Function