using constants

Hena has asked for the wisdom of the Perl Monks concerning the following question:

Hello Monks, I'm using some strings in a scripts as constants as they are strings used in parsing of file. But I've noticed a small oddity on this. So is this expected (couldn't find any reference in camel book on this).

> perl -we 'use constant K => 0;$array[0]="value";print $array[K],"\n"
+;'
value
> perl -we 'use constant K => KEY;$hash{"KEY"}="value";print $hash{K},
+"\n";'
Use of uninitialized value in print at -e line 1.
[download]

The array works as I expected. The hash does not. Is it better to use scalar even though it is not constant (used to do these that way)?

Comment on using constants Download Code

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Re: using constants by ikegami (Patriarch) on Oct 13, 2005 at 05:51 UTC
The quotes are optional on barewords used as hash elements. `$hash{key}` is the same as `$hash{'key'}` `$hash{shift}` is the same as `$hash{'shift'}` `$hash{K}` is the same as `$hash{'K'}` Use `$hash{K()}`, `$hash{&K}`, `$hash{(K)}` or `$hash{+K}` to work around the autoquoting. Update: I thought I'd add a link to the relevant documentation, but I can't find documentation on this. perldata mentioned the auto-quoting property of `=>`, but not of the hash index.	[reply] [d/l] [select]
Re^2: using constants by Hena (Friar) on Oct 13, 2005 at 05:57 UTC
Ah, Thanks. I Should have realised that :). Btw. Whats that + do? I understand the braces and &.	[reply]
Re^3: using constants by ikegami (Patriarch) on Oct 13, 2005 at 06:05 UTC
This question is in the docs. Specifically, perlop. Unary-`+` does nothing, but where `XXX` is a bareword, `+XXX` and `(XXX)` are expressions. Only barewords are auto-quoted, not expressions.	[reply] [d/l] [select]