Question

This is one of the most used Regex functions

Regex.IsMatch('Test text for regex test.', '(test)', RegexOptions.IgnoreCase | RegexOptions.Multiline); 

Can you explain how Regex.IsMatch method works ? I mean how it handles bitwise OR RegexOptions parameters ? How it defines method parameters ?

Thanks for replies !

Answer 1

RegexOptions is an enumeration with the [Flags] attribute applied to it. This allows bitwise operations to be applied to the various values.

You can also do something similar:

[Flags] enum MyOptions {    UpperCase = 1,    Reverse   = 2,    Trim      = 4 }  public static void DoTransform(MyOptions options) {     if ((options & MyOptions.UpperCase) == MyOptions.UpperCase) {         /* Do Upper case transform */     }     if ((options & MyOptions.Reverse) == MyOptions.Reverse) {         /* Do Reverse transform */     }     /* etc, ... */ }  DoTransform(MyOptions.UpperCase | MyOptions.Reverse); 

I’ve just done a bit more digging based on Frank’s comment and he is correct that with or without the [Flags] attribute, the code above will compile and run.

There have been other comments in regard to what the [Flags] attribute does not do but other than ‘it affects the ToString() result’ no one seems to know or wants to explain what it does do. In code I write, I adorn enumerations that I intend to use as bitfields with the [Flags] attribute, so in that case it is at least somewhat self-documenting. Otherwise, I’m at a loss.