I would like to evaluate a piece of code returning a positive integer and interpolate that in a '{}' quantifier in a regex, as in 
$string =~ /x{<code goes here>}/

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I have tried to do the code-evaluation bit via the (??..) construct, but something like, say 
$string =~ /(a+)x{(??{length $1})}/

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returns the dreaded Unescaped left brace in regex is deprecated here warning. I realize that this precise regex can be reworked into 
$string =~ /(a+)(??{$1 =~ s/a/x/gr})/

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to achieve the intended goal, but the point of the question is whether, nevertheless, there is some procedure that will allow code interpolation between non-literal regex braces.

In reply to interpolating code in regex brace quantifier by grobber

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