say length @many_strings;  # 1
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I think it should be pointed out that in this statement, length puts @many_strings into scalar context, thereby yielding 6 (as shown explicitly in the following line), and then 1 is returned because the length of the string “6” happens to be 1. With warnings enabled, this gives a warning, as it should:

17:09 >perl -wE "my @many_strings = ('abc', 'cd', 'e', 'fg', 'hi', 'he
+llo world'); say length @many_strings;"
length() used on @many_strings (did you mean "scalar(@many_strings)"?)
+ at -e line 1.
1
17:29 >
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For the record, in Raku swl’s use of reduce could be written:

use v6d;

my Str @many-strings = |<abc cd e fg hi>, 'hello world';

@many-strings.raku.put;
@many-strings.elems.put;

say [+] @many-strings.map: { .chars };
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Output:

17:09 >raku 2090_SoPW.raku
Array[Str].new("abc", "cd", "e", "fg", "hi", "hello world")
6
21

17:09 >
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using Raku’s built-in reduction metaoperator [+], documented here.

Hope that’s of interest,