After examining the code for a while, I wondered if VB.NET was optomizing the RegEx by reusing a version 'compiled' in realtime. To test this guess, I coded a new version that forced the RegEx to be declared for every iteration of the test loop by coding the loop before the call rather than after.
Imports System.Diagnostics
Imports System.Text.RegularExpressions
Public Class CompiledRegEx
Dim InlineTimeSpan As Integer
Dim CompiledTimeSpan As Integer
Dim LoopLimit As Integer
Dim PhoneNum(9999) As String
Dim I As Integer
Private Sub TimeEm_Click( ...
Dim myStopwatch As Stopwatch = New Stopwatch
Dim myTimeSpan As New TimeSpan
myStopwatch.Reset()
myStopwatch.Start()
If UseInline.Checked Then
For I = 0 To LoopLimit
UseInlineTest(I)
Next
End If
myStopwatch.Stop()
myTimeSpan = myStopwatch.Elapsed
InlineTimeSpan = myTimeSpan.Milliseconds
UsingInline.Text = myTimeSpan.ToString
myStopwatch.Reset()
myStopwatch.Start()
If UseCompiled.Checked Then
For I = 0 To LoopLimit
UseCompiledTest(I)
Next
End If
myStopwatch.Stop()
myTimeSpan = myStopwatch.Elapsed
CompiledTimeSpan = myTimeSpan.Milliseconds
UsingCompiled.Text = myTimeSpan.ToString
CalcImprovement()
End Sub
Private Sub UseInlineTest(ByVal I As Integer)
Dim myRegexString As New Regex( _
"^1?\s*-?\s*(\d{3}|\(\s*\d{3}\s*\))" & _
"\s*-?\s*\d{3}\s*-?\s*\d{4}$")
Dim RegExResult As Boolean
RegExResult = _
myRegexString.IsMatch(PhoneNum(I).ToString)
End Sub
Private Sub UseCompiledTest(ByVal I As Integer)
Dim myCompiledRegex As New myRegExNS.myRegExType
Dim RegExResult As Boolean
RegExResult = _
myCompiledRegex.IsMatch(PhoneNum(I).ToString)
End Sub
Private Sub CalcImprovement()
Try
Improvement.Text = _
CStr((InlineTimeSpan / CompiledTimeSpan))
Catch ex As Exception
Improvement.Text = ""
End Try
End Sub
Private Sub CompiledRegEx_Load( ...
Dim PhoneNumSuf As Integer = 0
Dim PhoneNumPre As String = "123-555-"
LoopLimit = CInt(NumberOfIterations.Text) - 1
For I = 0 To LoopLimit
PhoneNum(I) = PhoneNumPre & I.ToString.PadLeft(4, "0"c)
Next
End Sub
End Class
This time, the results were much closer to what I expected: about 7 1/2 times faster!
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The lesson here is that if you can avoid re-executing the statement that declares your RegEx, it will add more to your execution speed than even compiling the RegEx.
