CODEWITHSUNDEEP
regexpcre
hwnd
hwnd

Reputation: 70722

Special construct of expression use

With the construct of using If-Then-Else Conditionals in regular expressions, I would like to know the possible outcome of trying to manipulate many constructs into a single expression for multiple matches.

Let's take this example below.

foo(bar)?(?(1)baz|quz)

Now being combined with an expression, which matches the previous conditions and then we add on to the previous with the following conditions..

foo(bar)?(?(1)baz|quz)|(?(?=.*baz)bar|foo)

Mainly I am asking should you construct a regular expression in this way, and what would ever be the purpose that you would need to use it in this way?

Upvotes: 2

Views: 239

Answers (2)

zx81
zx81

Reputation: 41838

should you construct a regular expression in this way, and what would ever be the purpose that you would need to use it in this way?

In this case, and probably most cases, I would say "no".

I often find that conditionals can be rewritten as lookarounds or simplified within alternations.

For instance, it seems to me that the regex you supplied, 

foo(bar)?(?(1)baz|quz)|(?(?=.*baz)bar|foo)

could be replaced for greater clarity by

bar(?=.*baz)|foo(?:quz|barbaz)?

which gives us two simple match paths.

But it's been six months since you posted the question. During this time, answering a great many questions on SO, have you ever felt the need for that kind of construction?

Upvotes: 1

Michelle Welcks
Michelle Welcks

Reputation: 3894

I believe the answer to this would be ultimately be specific to the regex library being used or a language's implementation. ("Comparison of regular expression engines", Wikipedia.)

There isn't an official RFC or specification for regular expressions. And the diversity of implementations leads to frustration doing even "simple" expressions--the nuances you're considering are probably implementation-specific instead of regex-specific.

And even beyond your specific question, I think most of the regex-related questions on StackOverflow would be improved if people were more specific about the language being used or the library employed by the application they're using. When troubleshooting my own regular expressions in various applications (text editors for example) it took me awhile before I realized the need to understand the specific library being used.

Upvotes: 1

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