use constant {
    SEC   => 0,
    MIN   => 1,
    HOUR  => 2,
    MDAY  => 3,
    MON   => 4,
    YEAR  => 5,
    WDAY  => 6,
    YDAY  => 7,
    ISDST => 8,
};
[download]

I searched the doc on constant, and didn't see a good example, though

Dereferencing constant references incorrectly (such as using an array subscript on a constant hash reference, or vice versa) will be trapped at compile time.

Here's how it's done:

use constant Books_I_Own => 
{
    "The Wit and Wisdom of Mark Twain" => 1,
    "Attack of the Deranged Mutant Killer Monster Snow Goons" => 1,
    "Unix Power Tools" => 1,
}
[download]

  DB<2> x Books_I_Own
0  HASH(0x1c831b8)
   'Attack of the Deranged Mutant Killer Monster Snow Goons' => 1
   'The Wit and Wisdom of Mark Twain' => 1
   'Unix Power Tools' => 1
[download]

Yep. A limitation of that syntax is that, whilst the hash is a constant, it contents are not.

[14:26:14.28] c:\test>p1
use constant HASH=>{ a=>1, b=>2 };;
print %{ +HASH };;
a 1 b 2

HASH->{ c } = 3;;
print %{ +HASH };;
c 3 a 1 b 2

delete HASH->{ $_ } for keys %{ +HASH };;
print %{ +HASH };;
[download]

That can be solved using the same Hash::Util::lock_hash() method I mentioned above.

---

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.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."