Introduction
Eval3 library writen by Pascal Ganaye allows to parse and evaluate VB code, which is great but often it is not enough.What I needed was a class that would interprit a string that contains multiple expressions inclosed in square brakets.
For example this string:
GIS_[Format(Now, 'yy-MM-dd')]-[Field('ID')]-[Field('Source')]Will be evaluated to something like this:
GIS_10-01-13-5324523-DFS235FBackground
Lets assume we have an exprsion similar to the shown example above which we need to evaluate multiple times.I have writen a class that will parse the whole expression once and store "formulas" for future evaluations.
This sighnificantly reduces execution time while keeping it really simple
Using the code
Download Code: Eval3 Wrapper; Evalutation functionsIt is very easy to use EvalFormulaCollection class once you have Eval3 added to your project.
You just need to:
- Create new instance of
EvalFormulaCollectionclass with expression that you need to evaluate - Add "environment" object that provides functions that can be used in expression
- Call Initiate() method that will make reusable array of parsed "formulas".
- Call Value() property to get the interpreted value of the expression which is evaluated without parsing!
' Test evaluation of the expression with multiple VB Expressions
Sub Test()
Dim c As New MyClass
dim e as New evaluationFunctions
Dim expression As String = _
"GIS_[Format(Now, 'yy-MM-dd')]-[Field('ID')]-[Field('Source')]"
Dim ev as New EvalFormulaCollection(expression)
ev.AddEnvironment(c)
ev.AddEnvironment(e)
ev.Initiate()
MsgBox ev.Value()
End Sub
Points of Interest
The best thing about this code is its size. It is quite impressive what you can do withRegex class from RegularExpressions library with one line of code:' Find all expression in square brackets
Public Sub New(ByVal expression As String)
...
_matches = Regex.Matches(_expression, "[\[][^\[\]]{1,}[\]]")
End Sub
Posts
RSS Feed