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Re: Variable name
by almut (Canon) on Dec 08, 2008 at 15:08 UTC
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Are you, by any chance, using a lexical ('my') variable for $foo?
Symbolic references
only work with package variables:
#!/usr/bin/perl
use strict;
use warnings;
our $foo="foo";
my $bar="f";
no strict 'refs';
print ${$bar.'oo'}, "\n";
(BTW, just in case you're intending to create enumerated variables
like $var1, $var2, etc., consider using an array instead...)
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It worked !
Thanks a lot.
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Re: Variable name
by BrowserUk (Patriarch) on Dec 08, 2008 at 15:00 UTC
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... but it doesn't.
What does it do? (This is nearly always a more useful metric :)
I ask, because for me, (in the absence of strict), it works as expected whether I use globals or lexicals:
$foo = 'foo';;
$bar = 'f';;
print ${ $bar . 'oo' };;
foo
{
my $foo = 'foo';
my $bar = 'f';
print ${ $bar . 'oo' };
}
foo
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
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Really? It doesn't work for me with lexicals
My bad!
The output I showed was genuine, but all conducted in a single run of the debugger.
Which explains it, (though it doesn't exactly satisfy the concept of least surprise), as the globals also existed despite that I had created similarly named lexicals. Which, (apparently naively), I expected to override the globals at the local scope.
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
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Like I said:
"Use of uninitialized value in print"
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Re: Variable name
by johngg (Canon) on Dec 08, 2008 at 15:16 UTC
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I should use a hash instead, but humor me, would you ?
Well, just this once :-)
Actually, it works for me on the command line if not using strictures and not declaring the variables so they default to being package variables.
$ perl -le '
> $foo = q{foo};
> $bar = q{f};
> print ${$bar . q{oo}};'
foo
$
Enabling strictures and using lexical varables throws a "strict refs" error
$ perl -Mstrict -wle '
> my $foo = q{foo};
> my $bar = q{f};
> print ${$bar . q{oo}};'
Can't use string ("foo") as a SCALAR ref while "strict refs" in use at
+ -e line 4.
$
Turning the stricture off inside the print statement throws an "uninitialsed value" warning because you can't have soft references with lexical variables.
$ perl -Mstrict -wle '
> my $foo = q{foo};
> my $bar = q{f};
> print do {no strict q{refs}; ${$bar . q{oo}} };'
Use of uninitialized value in print at -e line 4.
$
Declaring the variables as package variables with our gets things working again.
$ perl -Mstrict -wle '
> our $foo = q{foo};
> our $bar = q{f};
> print do {no strict q{refs}; ${$bar . q{oo}} };'
foo
$
But having said all of that, you really should be using a hash and should avoid soft references like the plague if at all possible.
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Re: Variable name
by JadeNB (Chaplain) on Dec 08, 2008 at 22:37 UTC
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Everyone's been very helpful, so I think one of us is entitled to be cranky: Why are we humouring you (as opposed to linking to Why it's stupid to use a variable as a variable name)? That is, is this approach actually essential for some application, or were you puzzling out for “academic” interest why a construct wasn't working as expected (or is it some more sinister other, like that you're intending to use soft references after all?). | [reply] |
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In the OP's defense, there are still plenty of uses for symbolic references. Especially when you're building code that generates functions / classes / packages.
Symbolic refs are notoriously easy to get wrong, but perl's code-generation constructs are only just about adequate, and it's usually a case of either using symbolic refs or eval STRING, and eval STRING is usually just too messy (and slow).
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Re: Variable name
by MidLifeXis (Monsignor) on Dec 08, 2008 at 14:54 UTC
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$foo="foo";
$bar="f";
print ${$bar."oo"}, "\n";
Not certain what your issue is. Perhaps the output is being overwritten by your prompt. Try ending the print with a newline.
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perl -v
This is perl, v5.8.8 built for PA-RISC2.0
What version of perl are you using?
Also, is this part of a larger script (perhaps including use strict; use warnings;), or have you tried running this snippet as a standalone script?
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Nope, still doesn't work.
I am getting a 'Use of uninitialized value in print'
Maybe something else I am forgetting ?
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Re: Variable name
by f00li5h (Chaplain) on Dec 08, 2008 at 23:07 UTC
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use warnings; use strict;
my %f = ( oo => 'cats' );
print $f{ oo };
using an explicit hash instead of using the symbol table as a hash seems like the right thing to do ...
@_=qw; ask f00li5h to appear and remain for a moment of pretend better than a lifetime;;s;;@_[map hex,split'',B204316D8C2A4516DE];;y/05/os/&print;
Update would have worked just as well as a reply to Re^2: Variable name by Joost
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