Question

I have a complex regex, which contains constructs like this one:

"(" + sectionPattern + separatorPattern + ")*" + sectionPattern

The sectionPattern is a named group of complicated internal structure. Since sectionPattern appears twice, the long string defining this named group will be copied twice into the regex pattern. Moreover, because there is another, similar substructure inside sectionPattern, it will be copy-pasted four times, and so on. I couldn’t find a way to avoid such duplication, and the whole pattern is 4389 characters long now. It works, but I would prefer it being much-much shorter.

I thought there is a way to refer to an already defined named group in other parts of the pattern using only its name. I mean if you have a named group like this:

(?<sectionPattern>some_very_long_and_complicated_pattern)

…then you could refer briefly to it in other parts of the pattern like this:

(?<sectionPattern>)

I tried to use a “named backreference”:

\k<sectionPattern>

…but this matches only when the second match contains exactly the same text as the first one. Any solutions?

Answer 1

Unfortunately, there is no way to create a “reusable” pattern. You must repeat the pattern everywhere it’s needed.

However, here’s a better (more readable) way to compose those patterns:

var pattern = string.Format("({0}{1})*{0}", sectionPattern, separatorPattern);