Hi all,
When checking if the hash key exists, should I use defined() or just:
do_something if $hash{val}
I have done some tests and it seems there is no difference in
performance with or without defined(). When should defined() be used
then if it makes no difference?
TIA!
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Full Version: When to use defined
On Jul 5, 2005, at 12:15, Tielman Koekemoer ((TNE)) wrote:
| QUOTE |
| When checking if the hash key exists, should I use defined() or just: do_something if $hash{val} I have done some tests and it seems there is no difference in performance with or without defined(). When should defined() be used then if it makes no difference? |
Performance at that low-level rarely matters, when in doubt use
Benchmark.pm.
Take into account that a key can have undef as associated value in a
hash so those examples are not right indeed. The valid test in Perl is
do_something if exists $hash{key};
Sometimes one knows that the values of some particular hash are true,
in that case one relaxes a bit and writes
do_something if $hash{key};
but that's fragile. Note that I said "true", the value "0" is defined
but false, so that test would fail. Fragile, you see.
Thus, except for really quick and dirty short scripts I use exists()
when I mean exists().
-- fxn
Tielman Koekemoer (TNE) [TK], on Tuesday, July 5, 2005 at 12:15
(+0200) wrote these comments:
TK> I have done some tests and it seems there is no difference in
TK> performance with or without defined(). When should defined() be used
TK> then if it makes no difference?
did you tried:
$hash{val} = 0;
do something if $hash{val};
you should come to difference.
--
...m8s, cu l8r, Brano.
["That little droid and I have been through a lot together." - Luke]
(+0200) wrote these comments:
TK> I have done some tests and it seems there is no difference in
TK> performance with or without defined(). When should defined() be used
TK> then if it makes no difference?
did you tried:
$hash{val} = 0;
do something if $hash{val};
you should come to difference.
--
...m8s, cu l8r, Brano.
["That little droid and I have been through a lot together." - Luke]
Tielman Koekemoer (TNE) wrote:
| QUOTE |
| Hi all, |
Hello,
| QUOTE |
| When checking if the hash key exists, should I use defined() or just: do_something if $hash{val} I have done some tests and it seems there is no difference in performance with or without defined(). When should defined() be used then if it makes no difference? |
exists() tests whether the *key* exists while everything else tests the
*value* and in some contexts may autovivify the key.
This may help:
perldoc -q "What's the difference between "delete" and "undef" with hashes"
John
--
use Perl;
program
fulfillment
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