+972 52-548-6969
ChallengeThe regex that doesn’t match
time to read 1 min | 173 words
Can you make this test pass?
var expected = @"Cached query: SELECT this_.Id as Id5_0_, this_.Title as Title5_0_, this_.Subtitle as Subtitle5_0_, this_.AllowsComments as AllowsCo4_5_0_, this_.CreatedAt as CreatedAt5_0_ FROM Blogs this_ WHERE this_.Title = 'The lazy blog' /* @p0 */ and this_.Id = 1 /* @p1 */ "; Assert.True(Regex.IsMatch(expected, expected.Replace("5_", @"\d+_")));
I really don’t know what to think about this anymore….
More posts in "Challenge" series:
- (03 Feb 2025) Giving file system developer ulcer
- (20 Jan 2025) What does this code do?
- (01 Jul 2024) Efficient snapshotable state
- (13 Oct 2023) Fastest node selection metastable error state–answer
- (12 Oct 2023) Fastest node selection metastable error state
- (19 Sep 2023) Spot the bug
- (04 Jan 2023) what does this code print?
- (14 Dec 2022) What does this code print?
- (01 Jul 2022) Find the stack smash bug… – answer
- (30 Jun 2022) Find the stack smash bug…
- (03 Jun 2022) Spot the data corruption
- (06 May 2022) Spot the optimization–solution
- (05 May 2022) Spot the optimization
- (06 Apr 2022) Why is this code broken?
- (16 Dec 2021) Find the slow down–answer
- (15 Dec 2021) Find the slow down
- (03 Nov 2021) The code review bug that gives me nightmares–The fix
- (02 Nov 2021) The code review bug that gives me nightmares–the issue
- (01 Nov 2021) The code review bug that gives me nightmares
- (16 Jun 2021) Detecting livelihood in a distributed cluster
- (21 Apr 2020) Generate matching shard id–answer
- (20 Apr 2020) Generate matching shard id
- (02 Jan 2020) Spot the bug in the stream
- (28 Sep 2018) The loop that leaks–Answer
- (27 Sep 2018) The loop that leaks
- (03 Apr 2018) The invisible concurrency bug–Answer
- (02 Apr 2018) The invisible concurrency bug
- (31 Jan 2018) Find the bug in the fix–answer
- (30 Jan 2018) Find the bug in the fix
- (19 Jan 2017) What does this code do?
- (26 Jul 2016) The race condition in the TCP stack, answer
- (25 Jul 2016) The race condition in the TCP stack
- (28 Apr 2015) What is the meaning of this change?
- (26 Sep 2013) Spot the bug
- (27 May 2013) The problem of locking down tasks…
- (17 Oct 2011) Minimum number of round trips
- (23 Aug 2011) Recent Comments with Future Posts
- (02 Aug 2011) Modifying execution approaches
- (29 Apr 2011) Stop the leaks
- (23 Dec 2010) This code should never hit production
- (17 Dec 2010) Your own ThreadLocal
- (03 Dec 2010) Querying relative information with RavenDB
- (29 Jun 2010) Find the bug
- (23 Jun 2010) Dynamically dynamic
- (28 Apr 2010) What killed the application?
- (19 Mar 2010) What does this code do?
- (04 Mar 2010) Robust enumeration over external code
- (16 Feb 2010) Premature optimization, and all of that…
- (12 Feb 2010) Efficient querying
- (10 Feb 2010) Find the resource leak
- (21 Oct 2009) Can you spot the bug?
- (18 Oct 2009) Why is this wrong?
- (17 Oct 2009) Write the check in comment
- (15 Sep 2009) NH Prof Exporting Reports
- (02 Sep 2009) The lazy loaded inheritance many to one association OR/M conundrum
- (01 Sep 2009) Why isn’t select broken?
- (06 Aug 2009) Find the bug fixes
- (26 May 2009) Find the bug
- (14 May 2009) multi threaded test failure
- (11 May 2009) The regex that doesn’t match
- (24 Mar 2009) probability based selection
- (13 Mar 2009) C# Rewriting
- (18 Feb 2009) write a self extracting program
- (04 Sep 2008) Don't stop with the first DSL abstraction
- (02 Aug 2008) What is the problem?
- (28 Jul 2008) What does this code do?
- (26 Jul 2008) Find the bug fix
- (05 Jul 2008) Find the deadlock
- (03 Jul 2008) Find the bug
- (02 Jul 2008) What is wrong with this code
- (05 Jun 2008) why did the tests fail?
- (27 May 2008) Striving for better syntax
- (13 Apr 2008) calling generics without the generic type
- (12 Apr 2008) The directory tree
- (24 Mar 2008) Find the version
- (21 Jan 2008) Strongly typing weakly typed code
- (28 Jun 2007) Windsor Null Object Dependency Facility
Comments
Regex.IsMatch(expected, Regex.Escape(expected).Replace(@"5_", @"\d+_"))
The query contains regex characters which need to be escaped (i.e. '.').
It's a bit messy ... if this is going to be used a lot, would probably be good to replace the whitespace with '\s+', etc.
Michael: '.' will match any single character, so that will still work; it will just match more than expected.
I might guess that the newlines are confusing the regex engine.
But regex "/* " won't match string "/* ".
it's the /* */ comments...
Maybe Regex.Escape before you do your Replace might help...
It's a problem with the comment tags in the SQL statement. Remove the comments and the regular expression passes.
So, is Replace doing something funny to the asterisk or what?...
Aren't tests supposed to be readable? I have no idea what this is supposed to do from staring at the code. Might be just me though.
Regex.IsMatch(expected,Regex.Escape(expected).Replace("5_", @"\d+_"))
passes
There isn't anything wrong with the string, but that regex will never work, as it's going to change all the digits to 5. Should be this: @"\d+_(?=0)" That does a lookahead and only matches digits followed by an _ then a 0. The 0 is then not part of the grouping and so won't be changed.
It doesn't make sense, why would you want to do that anyway?
SELECT this_.Id as Id5_0_,
FROM Blogs this_
WHERE this_.Title = 'The lazy blog' /* @p0 */
@Chris I was only providing one example of what would be escaped. As Sergey and bobo mentioned, the comment tags also cause an issue because '*' is a regex quantifier, and as such, is escaped by Regex.Escape as well.
Bertrand,
Well, when you only see a very small part, it is not surprising
Cool. That part does look convoluted :)
Why would we care about the regex when the entire principle this is based on is a big hairy WTF?
FYI - I know the multiline syntax is handy from a readability perspective, but tests like that may not pass on Mono/Linux or any other OS that doesn't use \r\n as the line terminator:
www.cornetdesign.com/.../...nvironmentnewline.html
To get it to pass, you'd have to recompile on the platform. Well, unless you are developing this on Mono/Linux, but I don't think that's the case. :)
Cory,
Yes, I know about that, but since this is a WPF app, and Mono doesn't have that, I don't worry too much about it
Don't know if you're still having issues here, but it looks like you need to escape the '' and '.' characters in the pattern. Also, you probably need to compact the whitespace in the pattern to as few as possible, then replace them with \s
Ooops, didn't see James' comment above... and it looks like it works.
The Regex.Escape() method does pretty much what I described above. From the docs: "Escapes a minimal set of characters (\, *, +, ?, |, {, [, (,), ^, $,., #, and white space) by replacing them with their escape codes."
That's handy.
Comment preview