Re: How do I efficiently predeclare a hash with a set of keys

This is concise ~~and saves a little space by not allocating any to the values.~~* The keys however still exist and test as such with exists.

my %set; 
undef @set{ 5,6,8..53,62..106 };
[download]

Update: This used to make a difference at some point in the past, but it no longer does (circa. 5.8.8 and possibly before).

The null list assignment method others have described my %set; @set{ ... } = (); is equal in memory usage and actually slightly faster. Thanks to bart++ for bringing this to my attention.

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Re^2: How do I efficiently predeclare a hash with a set of keys by bart (Canon) on May 19, 2007 at 09:30 UTC
How does this compare, for speed and memory use, to `@set{ 5,6,8..53,62..106 } = ();` [download] ? I'd expect them to be comparable.	[reply] [d/l]
Re^3: How do I efficiently predeclare a hash with a set of keys by BrowserUk (Patriarch) on May 19, 2007 at 10:07 UTC
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."	[reply] [d/l]
Re^2: How do I efficiently predeclare a hash with a set of keys by lupey (Monk) on May 18, 2007 at 19:42 UTC
Thank you. This is exactly what I wanted :)	[reply] [d/l]