my $clist; 
BEGIN { 
    $clist = {a => 1, b => 2}; 
} 
use constant $clist;
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That's what I meant by being more 'expansive'... compared to

my $clist;
use <anymodule> ($clist = {a => 1, b => 2});
use constant $clist;
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Note -- # anymodule, above, works for modules that are guaranteed to never cause some conflict with random assign statements in its argument list, like "mem".

It is a secondary use of mem, but still one that's useful to know if you don't want to have your header/use/init area littered w/compiler-keywords like BEGIN and indentation that sticks out like a wart. Some people don't care about those things, some do. Chocolate or butterscotch, take your pick. ;-)

Of course all that could be handled in a greatly more straightforward manner if perl had a Macro facility like most compiler languages. While you can do similar w/perl using filters, my impression is that those are frowned upon, leaving no alternatives (or at least none that I'm aware of) :-(.