Is ?: something special in regex?

[Tsukihime]

Looking at some of yanfly's regex

/<(?:REGION_BATTLEBACKS|region battlebacks)>/iI don't understand what the ?: is doing.Is there something special about it in the context of a capture group?

 

[Zalerinian]

I'm also interested in knowing. I know that :? Would mean zero or one :, but I'm not sure about ?:

 

[Solistra]

?: allows you to create match groups that capture matches without generating back-references. Basically, it's a performance optimization when you don't need access to all of the back-references that your regular expression creates -- just the most recent one.

 

[Tsukihime]

Thanks, I see how it works.


http://rubular.com/r/OoeCIxDhOm


Though, does that performance optimization also apply when you only have one capture group?

 

[Solistra]

It certainly can, depending on the string you're matching the regular expression against.

 

[Tsukihime]

Is there a term for that notation?

 

[Solistra]

Honestly, I don't know -- and I don't really see the importance of knowing the term if you know what you're doing with it, really.

 

[Tsukihime]

It certainly can, depending on the string you're matching the regular expression against.

What kind of strings/regex would fit that bill?

I guess I'm not really understanding the point of using ?: because in this context the particular note-tag is only used as a delimiter of some sort; the captured contents are never being used anyways. So it's probably a bad example.

Some may be tempted to think that for some reason this

(?:VALUE)

is better over just

VALUE

 

[Shaz]

Would be useful if you just want to detect if the string exists. So for things you're setting in notes as a flag but don't have any parameters, or for the purposes of that particular section of script, you don't care what the parameters are.

 

[Solistra]

Basically, you wouldn't be using ?: for capturing a single flat value -- the point is to optimize grouping, and you certainly wouldn't need to group something like VALUE. What you're doing with ?: is minimizing the memory footprint of running a regular expression where all of the back-references that would normally be generated are legitimately unnecessary. In the example, Yanfly's regular expression matches REGION_BATTLEBACKS and region battlebacks (including all of those case-insensitive variations). Essentially, that had to be defined as a group in order to match what was needed: a group was required, but all of the back-references generated by using it were not.


Edit: Just saw this.

Would be useful if you just want to detect if the string exists. So for things you're setting in notes as a flag but don't have any parameters, or for the purposes of that particular section of script, you don't care what the parameters are.

Then you could just use string['match this'].

 

[TheoAllen]

Looking at some of yanfly's regex

/<(?:REGION_BATTLEBACKS|region battlebacks)>/iI don't understand what the ?: is doing.Is there something special about it in the context of a capture group?

That's mean you can write your notetag like this

<ReGiOn BaTtLeBaCkS>Correct me if I'm wrong

 

[Shaz]

Yes, because of the /i at the end. That's got nothing to do with the ? at the start.

 

[Solistra]

That's mean you can write your notetag like this

<ReGiOn BaTtLeBaCkS>Correct me if I'm wrong

No offense, but you are incorrect. That's what the i flag at the end of the regular expression does -- it allows it to match regardless of case. (The "i" stands for "insensitive," as in "case insensitive.")

Edit: Again, the point of using ?: is to make use of match groups without generating the back-references. It's about performance.

 

[TheoAllen]

No offense, but you are incorrect. That's what the i flag at the end of the regular expression does -- it allows it to match regardless of case. (The "i" stands for "insensitive," as in "case insensitive.")

Edit: Again, the point of using ?: is to make use of match groups without generating the back-references. It's about performance.

Well, that's something new for me ._.

Thanks anyway

 

[estriole]

/<(?:REGION_BATTLEBACKS|region battlebacks)>/imeans we can write it as

<region_battlebacks>

or

<region battlebacks>

(one using space one using underscore)

so we could also use it as

/<(?:REGION_BATTLEBACKS|region battlebacks|rb|reg_battleb)>/iand we can use <rb> and <reg_battleb>

i think ?: is like "if either regexp inside the bracket match" it will grab the data.

(but it might also means just plain if and the | is the one making the or statement)

i have no actual knowledge about regexp. but it's based on experience on experimenting on regexp (combining victor, yanfly, tsukihime, mr bubble) to make my own notetags grabber script. i usually use trial and error and see what happen when we put that regexp. and i found above when seeing mr bubble script. in his notetags we can use item, armor, weapon or just i, a, w (for shorter notetags).

 

[Tsukihime]

i think ?: is like "if either regexp inside the bracket match" it will grab the data.

No, it is what solistra has said up there.


The pipe | in the parentheses is the one that says either-or.


There are no if conditions in regex, which is why regex is not suitable for certain applications.

 

[Shaz]

Since the original question has been answered ...


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