You can do it the other way around with Lexical::Alias for lexicals (only the scalar variable needs to be lexical). This doesn't use tie. 

use Lexical::Alias;
my ($s, %h);

alias $h{key}, $s;
print \$s, "\n", \$h{key}, "\n";

=>

SCALAR(0x811e2f4)
SCALAR(0x811e2f4)

[download]

Don't use $a and $b for variable names. They have special meanings.

Update(s): To make it clear once and for all: the code above makes the lexical scalar variable $s an alias for $h{key}. The syntax is alias <src>, <dst>. This confuses many people, because it's different from common functions like push @ary, ... or index $str, ... etc. where object comes first. Here's a paragraph from the POD:

Version 0.04 introduced the $Lexical::Alias::SWAP variable. When it is true, the arguments to the aliasing functions are expected in reverse order; that is, the alias comes first, and the source variable second.

(Thanks to Jenda from perlmonks.org for requesting this.)

I don't recommend using SWAP though, it induces more unmaintainability and confusion.

In reply to Re: Make hash key an alias by calin
in thread Make hash key an alias by pope

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