Evaluate
Runs a compiled expression and returns its current value.
Syntax: expression.Evaluate()
- expression
- required An object expression that evaluates to an ITbExpression, typically the value returned by Compile.
The return value is a Variant holding the result of the expression. Its subtype reflects the natural type of the value — for example, Double for a numeric expression, String for a text-producing one, Boolean for a comparison.
Each call re-runs the expression against the current state of its bindings. If the bound objects expose properties whose values can change between calls — host application state, the current row of a recordset, configurable parameters — evaluating the same compiled expression twice may legitimately return different values.
A run-time error raised inside the expression — division by zero, type mismatch, an invalid call into a bound object — propagates out of Evaluate like any other run-time error.
Example
This example compiles an expression that references a property on the host object via AddCustomBinderObject, then evaluates it twice with the property having different values.
' In the host class:
Public Counter As Long
Public Sub EvaluateTwice()
Dim Service As TbExpressionService = New TbExpressionService
Service.AddStdLibraryBinder()
Service.AddCustomBinderObject "State", Me, IsAppObject
Dim Expr As ITbExpression = Service.Compile("Counter * 2")
Me.Counter = 1 : Debug.Print Expr.Evaluate() ' 2
Me.Counter = 5 : Debug.Print Expr.Evaluate() ' 10
End Sub