G'day Hauke,
++ This looks like a very good start; seems reasonably complete; and covers most of the points I might have made. I have comments on two areas, as follows.
With any sort of tutorial, those reading it — to learn about the subject, rather than for reviewing, proof-reading, etc. — probably start with limited knowledge. Accordingly, any terms used should be unambiguous; unfortunately, you've used $regex to mean two different things:
$regex = join ... $regex = qr/...
I'm familiar with both the subject matter and the technique, so this posed no problem for me; however, for someone learning this, it may do. While it's reasonably obvious in the short code example, half a page later, in the middle of descriptive text, the appearance of $regex might not be as obvious to the student as it is to you or I. Consider renaming those; purely as a suggestion:
$regex_base_str = join ... $regex_compiled = qr/...
In points (4) & (5), in the first list, you show grouping. To resolve the same issue in both, you use explicit capture grouping in (4), and implicit non-capture grouping in (5).
Regex pieces used for alternation often occur as part of a larger regex; in fact, I suspect that's the more usual case. This may be as simple as the anchor assertions you show in (4), or could be a lot more complex. I'd suggest adding explicit non-capturing grouping to $regex_base_str (or whatever you call it) as part of the normal technique. To demonstrate:
# Simple case: OK - matches "a" or "b" $ perl -E 'my $re = "a|b"; $re = qr{$re}; say $re' (?^u:a|b) # Complex case: NOT OK - matches "Xa" or "bY" $ perl -E 'my $re = "a|b"; $re = qr{X${re}Y}; say $re' (?^u:Xa|bY) # Complex case: OK - matches "a" or "b" [fixed with "(?:...)"] $ perl -E 'my $re = "(?:a|b)"; $re = qr{X${re}Y}; say $re' (?^u:X(?:a|b)Y)
— Ken
In reply to Re: [RFC] Building Regex Alternations Dynamically
by kcott
in thread Building Regex Alternations Dynamically
by haukex
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