Re: No need to escape right brace in regex

I don’t know why, but this behaviour is apparently by design:

A literal "{" should now be escaped in a pattern

If you want a literal left curly bracket (also called a left brace) in a regular expression pattern, you should now escape it by either preceding it with a backslash ("\{") or enclosing it within square brackets "[{]", or by using \Q; otherwise a deprecation warning will be raised. This was first announced as forthcoming in the v5.16 release; it will allow future extensions to the language to happen.

— perl5211delta#Deprecations

Presumably the planned “future extensions to the language” (whatever they are) won’t be affected by unescaped right braces.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^2: No need to escape right brace in regex by no_slogan (Deacon) on Oct 21, 2014 at 06:57 UTC
`{` is only special if it's followed by `/\d+,?\d*}/`. If they want to add anything else that can go between `{ }`, they have to either add a simple rule to the language (always backslash `{` unless you want special behavior), or a bunch of weird rules that they might want to change again later. `}` is never special unless a preceding `{` makes it so.	[reply]
Re^3: No need to escape right brace in regex by syphilis (Archbishop) on Oct 21, 2014 at 08:14 UTC
But you don't always get the deprecation warning: `C:\>perl -le "$_ =~ /{}/;" C:\>perl -le "$_ =~ /.+{}/;" C:\>perl -le "$_ =~ /a+{}/;" C:\>perl -le "$_ =~ /(a+)?{}/;" C:\>perl -le "$_ =~ /a{}/;" Unescaped left brace in regex is deprecated, passed through in regex; +marked by <-- HERE in m/a{ <-- HERE }/ at -e line 1. C:\>perl -le "$_ =~ /\d{}/;" Unescaped left brace in regex is deprecated, passed through in regex; +marked by <-- HERE in m/\d{ <-- HERE }/ at -e line 1. C:\>` [download] That behaviour fits ok with the (undetailed) documentation that Athanasius found, but does it tie in at all with the cases you're describing ? (I don't see the connection, though that doesn't mean there isn't one :-) Cheers, Rob	[reply] [d/l]
Re^4: No need to escape right brace in regex by LanX (Saint) on Oct 21, 2014 at 09:28 UTC
This is really a bit strange. Looks like they are only simplifying parsing of quantifiers like in `/a{1,2}/` to avoid look ahead analysis. All other cases you've shown can not be quantifiers. Maybe the warning should be better phrased? Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :)}	[reply] [d/l]
Re^3: No need to escape right brace in regex by LanX (Saint) on Oct 21, 2014 at 10:18 UTC
Hmm I think it's even more complicated, there is still `(?{code})` and `(??{code})` to handle. But yes looks like they are cleaning up some messi parsing rules. Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :)}	[reply] [d/l] [select]
Re^4: No need to escape right brace in regex by syphilis (Archbishop) on Oct 21, 2014 at 10:34 UTC
But yes looks like they are cleaning up some messi parsing rules It does look that way - I guess all will become clear eventually. In the meantime I'll just escape both '{' and '}'. The same warning showed up with the advent of 5.18 (or was it 5.20) and I eradicated those warnings (by escaping the braces) accordingly. But 5.21.x has uncovered other situations where braces are unacceptably unescaped - situations that 5.20 and earlier didn't care about. Cheers, Rob	[reply]
Re^5: No need to escape right brace in regex by LanX (Saint) on Oct 21, 2014 at 10:58 UTC