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Re: map a list - segfault

by imp (Priest)
 on Mar 12, 2007 at 20:00 UTC ( #604422=note: print w/replies, xml ) Need Help??

in reply to map a list

The block that caused the segfault doesn't work the way you think it does, because of precedence:
```perl -MO=Deparse -e '
(@n=(1,2) && (\$n[1],\$n[0]));
(@n=(1,2) && (\$n[1],\$n[0]));
(@n=(1,2) && (\$n[1],\$n[0]));
'
@n = ('???', 2) && (\$n[1], \$n[0]);
@n = ('???', 2) && (\$n[1], \$n[0]);
@n = ('???', 2) && (\$n[1], \$n[0]);
Using 'and' instead of && would work, or an extra set of parens.
```perl -MO=Deparse -e '
(@n=(1,2) && (\$n[1],\$n[0]));
((@n=(1,2)) && (\$n[1],\$n[0]));
(@n=(1,2) and (\$n[1],\$n[0]));
'
@n = ('???', 2) && (\$n[1], \$n[0]);
\$n[1], \$n[0] if @n = (1, 2);
\$n[1], \$n[0] if @n = (1, 2);

As for the segfault itself, I don't grok why it breaks but Devel::Peek gives a hint:

```perl -MDevel::Peek -le '
(@n=(1,2) && (\$n[1],\$n[0])); print Dump \@n;
(@n=(1,2) && (\$n[1],\$n[0])); print Dump \@n;'
SV = RV(0x3c02b018) at 0x3c0062dc
REFCNT = 1
FLAGS = (TEMP,ROK)
RV = 0x3c011718
SV = PVAV(0x3c0084dc) at 0x3c011718
REFCNT = 2
FLAGS = ()
IV = 0
NV = 0
ARRAY = 0x3c02a4f0
FILL = 1
MAX = 3
ARYLEN = 0x0
FLAGS = (REAL)
Elt No. 0
SV = NULL(0x0) at 0x3c006168
REFCNT = 1
FLAGS = ()
Elt No. 1
SV = NULL(0x0) at 0x3c006264
REFCNT = 1
FLAGS = ()

SV = RV(0x3c02b018) at 0x3c0062dc
REFCNT = 1
FLAGS = (TEMP,ROK)
RV = 0x3c011718
SV = PVAV(0x3c0084dc) at 0x3c011718
REFCNT = 2
FLAGS = ()
IV = 0
NV = 0
ARRAY = 0x3c02a4f0
FILL = 1
MAX = 3
ARYLEN = 0x0
FLAGS = (REAL)
Elt No. 0
SV = UNKNOWN(0xff) (0x0) at 0x3c006168
REFCNT = 1
FLAGS = ()
Elt No. 1
SV = UNKNOWN(0xff) (0x0) at 0x3c006264
REFCNT = 1
FLAGS = ()
Note that the array entries changed from :
```SV = NULL(0x0) at 0x3c006168
To:
```SV = UNKNOWN(0xff) (0x0) at 0x3c006168

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 [ambrus]: Corion: ah, so you want a library that parses HTTP, and you want to do the IO yourself, and don't want a full AnyEvent wrapper. [ambrus]: Corion: I think I parsed a HTTP header from a string with LWP once. You can definitely use that to create a HTTP message too. The problme is [ambrus]: that if you do that, you'd have to find where each HTTP response ends, which is nontrivial if you want persistent connections (essential for performance if you have small requests). [Corion]: ambrus: Yes, ideally an API that I feed the incoming data piece by piece and that I can ask "is that response done" and "what should I do next" and "please construct the appropriate redirect for me" [Corion]: ambrus: Yes, ideally the module would do all that nasty stuff for me and give me a way to ask it what the current situation is [ambrus]: Corion: you could also consider using some wrapper over the multi interface of curl, I think Net::Curl might be a good one, since implementing enough of what it expects from the event loop might be easier than a full AnyEvent interface. [ambrus]: Corion: you could also consider using IO::Async and its POE driver and some HTTP module for it, but I don't know if that would solve your problems with AnyEvent+POE [ambrus]: Corion: wait, you didn't say POE. You said Prima, let me look up what that is. [ambrus]: Corion: have you considered just writing an AnyEvent integration for that thing? [ambrus]: Or perhaps pushing schmorp to write one?

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