Course of Raku / Regexes and grammars / Regexes / Captures

Named captures

Numbered captures are handy, but when a pattern grows, names are clearer than numbers. To give a capture a name, write $<name>=( … ):

if 'Anna:30' ~~ / $<name>=(\w+) ':' $<age>=(\d+) / {
    say $<name>; # ｢Anna｣
    say $<age>;  # ｢30｣
}

The captured pieces are now reached by name through $<name> and $<age> instead of $0 and $1. This is the same as writing $/<name>, because the names live inside the match variable $/.

Named captures make a pattern read almost like a description of the data:

if 'x=5' ~~ / $<key>=(\w+) '=' $<value>=(\w+) / {
    say "key is $<key>, value is $<value>"; # key is x, value is 5
}

As with positional captures, each named capture is a match object, so $<age>.Str gives the plain text and $<age>.from gives its position.

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