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From: Gibbering on 15 Apr 2008 15:46
I want to access some data from a hash, but want to build that hash's
name on the fly... here's the code:

%hello = (a => 'doggy');
print ${'hell' . lc 'O'}{a};

does the trick as does:
print %{'hell' . lc 'O'}->{a};

however, under "use strict", this fails, since %hello isn't declared
with "my".

If I do put a my in front of the %hello declaration, the print
statement gives me nothing.
I have a sinking suspicion that the above code is wrong, dangerous,
and error prone since I'm not even sure why it works.

What is the proper way to do such a thing?
From: xhoster on 15 Apr 2008 15:56
Gibbering <roblund(a)gmail.com> wrote:
> I want to access some data from a hash, but want to build that hash's
> name on the fly... here's the code:

Most likely, you want a multi-level hash.

>
> %hello = (a => 'doggy');
> print ${'hell' . lc 'O'}{a};
>
> does the trick as does:
> print %{'hell' . lc 'O'}->{a};

my %hash;
$hash{hello} = {a => 'doggy'};

print $hash{'hell' . lc 'O'}->{a};


> however, under "use strict", this fails, since %hello isn't declared
> with "my".

Yes indeed, that is one the of things that use strict is there for. The
main one, even.

>
> If I do put a my in front of the %hello declaration, the print
> statement gives me nothing.

You are using two different variables. The lexical %hello, and the global
%main::hello. Since lexicals can't be accessed symbolically, your attempt
at symbolic access (in the absence of use strict) resolved to %main::hello.

Xho

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From: J�rgen Exner on 15 Apr 2008 16:08
Gibbering <roblund(a)gmail.com> wrote:
>I want to access some data from a hash, but want to build that hash's
>name on the fly... here's the code:
>
>%hello = (a => 'doggy');
>print ${'hell' . lc 'O'}{a};
>
>does the trick as does:
>print %{'hell' . lc 'O'}->{a};
>I have a sinking suspicion that the above code is wrong, dangerous,
>and error prone since I'm not even sure why it works.

See gazillions of previous articles about 'symbolic reference'.
Or just perldoc -q variable ' How can I use a variable as a variable
name?'

>What is the proper way to do such a thing?

Use your own hash instead of the system symbol table. In your case
becasue that would become a HoH (hash of [ref to] hash).

jue
From: smallpond on 15 Apr 2008 16:09
On Apr 15, 3:46 pm, Gibbering <robl...(a)gmail.com> wrote:
> I want to access some data from a hash, but want to build that hash's
> name on the fly... here's the code:
>
> %hello = (a => 'doggy');
> print ${'hell' . lc 'O'}{a};
>
> does the trick as does:
> print %{'hell' . lc 'O'}->{a};
>
> however, under "use strict", this fails, since %hello isn't declared
> with "my".
>
> If I do put a my in front of the %hello declaration, the print
> statement gives me nothing.
> I have a sinking suspicion that the above code is wrong, dangerous,
> and error prone since I'm not even sure why it works.
>
> What is the proper way to do such a thing?

This should answer some of your questions
perldoc -q 'How can I use a variable as a variable name?'

But why name this hash at all? Why not use an anonymous hash?
To be useful, you need a reference to it anyway.
--S
From: Chris Mattern on 15 Apr 2008 17:47
On 2008-04-15, Gibbering <roblund(a)gmail.com> wrote:
> I want to access some data from a hash, but want to build that hash's
> name on the fly... here's the code:

For God's sake, *why*?
>
> %hello = (a => 'doggy');
> print ${'hell' . lc 'O'}{a};
>
> does the trick as does:
> print %{'hell' . lc 'O'}->{a};
>
> however, under "use strict", this fails, since %hello isn't declared
> with "my".
>
> If I do put a my in front of the %hello declaration, the print
> statement gives me nothing.
> I have a sinking suspicion that the above code is wrong, dangerous,
> and error prone since I'm not even sure why it works.
>
> What is the proper way to do such a thing?

By not doing it and using a hash of hashes instead.


--
Christopher Mattern

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