Good call. At some point in the past, the undef version used less memory and was faster than the null list assignment version. If I remember correctly, it was tilly that pointed this out to me.

However, I just tried it with 5.8.8 and that is no longer the case. They both use the same amount of memory, and the null list assignment is marginally (~4%) faster. It's still faster and uses less memory than the typical method. 

my %set = map{ $_ => 1 } 1, 2, 5..8, 100..200;

[download]

Another case of How do I know what I 'know' is right?. :( I'll update my node above to reflect this.

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."

In reply to Re^3: How do I efficiently predeclare a hash with a set of keys by BrowserUk
in thread How do I efficiently predeclare a hash with a set of keys by lupey

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