How to flatten or stringify an object (esp. Match)?

~ is the Str contextualizer:

'foobar' ~~ m{ (foo) };
say ~$0

will directly coerce it to a Str. You can use that if you have many matches, i. e.:

'foobar' ~~ m{ (f)(o)(o) };
say $/.map: ~*; # (f o o)

The constructor for Str takes any Cool value as argument, including a regex Match object.

'foobar' ~~ m{ (foo) };
say $0.WHAT; # (Match)
say $0.Str.WHAT; # (Str)

Just treat the objects as if they were strings.

If you apply a string operation to a value/object Raku will almost always just automatically coerce it to a string.

String operations include functions such as print and put, operators such as infix eq and ~ concatenation, methods such as .starts-with or .chop, interpolation such as "A string containing a $variable", and dedicated coercers such as .Str and Str(...).

A Match object contains an overall match. Any "children" (sub-matches) are just captures of substrings of that overall match. So there's no need to flatten anything because you can just deal with the single overall match.

A list of Match objects is a list. And a list is itself an object. If you apply a string operation to a list, you get the elements of the list stringified with a space between each element.

So:

'foobar' ~~ m{ (f) (o) (o) };
put $/;          # foo
put $/ eq 'foo'; # True
put $/ ~ 'bar';  # foobar
put $/ .chop;    # fo
put "[$/]";      # [foo]
put $/ .Str;     # foo

my Str() $foo = $/;
say $foo.WHAT;   # (Str)

put 'foofoo' ~~ m:g{ (f) (o) (o) }; # foo foo