Front page | perl.perl5.porters |
Postings from August 2011
I've been giving some thought to the semantics behind re_evals, as regards
their behaviour regarding lexical vars and closure; i.e. when do they get
(re)compiled, and what instances of lexical vars to they capture each
time, etc.
I've worked this up into a big series of TODO tests in the davem/re_eval
branch, and the commit message (shown below) summarises the basic
principles of how I think it should eventually work.
Can anyone see anything wrong with this?
commit e04b85764f6d15d12d2a25b56d117f71c4ce6f51
Author: David Mitchell <davem@iabyn.com>
AuthorDate: Mon Aug 8 17:56:10 2011 +0100
Commit: David Mitchell <davem@iabyn.com>
CommitDate: Tue Aug 9 15:29:22 2011 +0100
re_eval and closures: add lots of TODO tests
re_evals currently almost always do the wrong thing as regards what
lexical variable they refer to. This commit adds lots of TODO tests that
show what behaviour I think there should be. Note that because hardly any
of these tests pass yet, I haven't been able to verify whether they have
any subtle typos etc.
The basic philosophy behind these tests is:
* literal code is compiled once at compile-time and shares the same
lexical environment as its surroundings; i.e.
/A(?{..$x..})B/
is like
/A/ && do {..$x..} && /B/
* qr is treated as a closure: compiling once, but capturing its
environment anew each time it is instantiated; i.e.
for my $x (...) { push @r, qr/A(?{..$x..}B)/ }
is like
for my $x (...) { push @r, sub { /A/ && do {..$x..} && /B/ } }
* run-time code is recompiled each time the regex is compiled; literal
code in the same expression isn't recompiled; i.e.
$code = '(?{ BEGIN{$y++} })';
for (1..3) { /(?{ BEGIN{$x++}})$code/ }
# x==1, y==3
* an embedded qr is not stringified, so the qr retains its original
lexical environment; i.e.
$x = 1;
{ my $x = 2: $r = qr/(??{$x})/ }
/A$r/; # matches A2, not A1
Affected files ...
M t/re/pat_re_eval.t
--
It's not that I'm afraid to die, I just don't want to be there when it
happens.
-- Woody Allen
Thread Next