CODEWITHSUNDEEP
regex-lookaroundsraku
jakar
jakar

Reputation: 1701

"Nothing" in Lookaround terms [RAKU]

I was reading in regexes documemtation about "Tilde for nesting structures".

The sideline explanation about the use of <?> is:

Here <?> successfully matches the null string.

I assumed that I was able to use <?[]> instead of it, but it failed to do so!

As an example:

say so "" ~~ / <?> /;
say so "test" ~~ / <?> /;

say so "" ~~ / <?[]> /;
say so "test" ~~ / <?[]> /;

The response:

True
True

False
False

Could someone give me an explanation about this?

Upvotes: 5

Views: 108

Answers (1)

Jonathan Worthington
Jonathan Worthington

Reputation: 29454

The syntax <?[]> means a lookahead matching an empty character class. Observe that an empty character class also never matches:

say "x" ~~ /<[]>/   # Nil

A character class specifies a set of characters that could be matched. An empty character class implies an empty set of characters, and so cannot possibly match anything.

Upvotes: 10

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