Does using undef as hash values save any memory in Perl? -

-

a Perl idiom to remove duplicate values ​​from an array: 

  @uniq = Keys% {{Map {$ _ = & gt; 1} @list}}

Using this version is cheaper: 

  @uniq = keys% {{Map {$ _ = & gt; ; Undef} @list}} I have tested with these one-liners, and it seems that this is true on some versions of Perl:  
  Perl -e 'my% x; $ X {$ _} = 1 for 0.000000; System "ps -ovsz $$" 'perl -e' my% x; Unfifferent for $ X {$ _} = 0..1000_000; System "ps -ovsz $$" '

OK, undef < / Code> is considered a flyweight value, which means that all its references indicate the same figure. You do not do this for other verbal people, you still need the upper part of the slot, though it is mentioned though. However, I do not see any memory for me on Perl 5.10 or 5.11 on Mac OS X. While the perl in is undef can not use more memory in the case, expected me to make sure it uses more memory, so it takes hold anyway . However, I am not eager to investigate memory usage in internals.

It is very useful to show these types of things 

  Use # Pearl Devel !:: Peak; My $ a = lower; My $ b = uncle; Dump ($ A); Dump ($ B); My% hash = map {$ _, anonymous} 1 .. 3; $ Hash {4} = 'hello'; Dump (\% hash);

The output looks a bit scary at first, but let's see that the undef values ​​are zero (0x0) instead of individual strings 0x100208708 REFCNT = 1 FLAGS = (PADMY) SV = nULL (0x0) REFCNT = 1 price Flags on 0x100208738 ( PV ): 

  SV = nULL (0x0) 0x100805008 Arfsiatti = 1 flags = (TAMP, Aroke) RV = 0xl00208780 SV = Piviacvi (0x10080 9 8 8) REFCNT = 2 flags = on 0xl00208780 (Padmi, Seyrijh) RRE = 0x100202200 (0: 5) = 0 (0: 00805018 ) 0x100805008 = = (PADMY) SV = RV (0x100805018), 1: 2, 2: 1) hash quality = 91.7% KEYS = 4 filling = 3 Max = 7 Riter = -l Eiter = 0x0 ELT "4" HASH = 0xb803eff9 SV = PV (0x100801c78) 0x100804ed0 REFCNT = 1 the FLAGS = (PoK, pPOK) PV = 0x100202a30 "Hello" \ 0 CUR = 5 LEN = 8 ELT "1" HASH = 0x806b80c9 SV = zero (0x0) = 1 FLAGS = (on 0x100820db0 REFCNT) "3" HASH = 0xa400c7f3 REFCNT = 1 Flags = ()
on SV = ELT Zero (0x0) 0x100820df8

Comments

Post a Comment

Popular posts from this blog

oracle - The fastest way to check if some records in a database table? -

-
I have a big table to work with. I have to see that there are some records whose parent_id is equal to my passing value. Currently I do this by implementing "my_table using select count (*) where parent_id =: id"; If the result> 0, it means that they exist. Because this is a very large table, and I do not care what the actual number of records present, I just want to know if it exists, so I think count (*) Bit is disabled. How do I apply this requirement most quickly? I'm using Oracle 10. # Tips for Hibernation & amp; Tricks It suggests writing in such a way: Integer number = (integer) session .createQuery ("Select Count (*) to ...."). UniqueResult (); I do not know what is the magic of the unique rule? Why does it fast? To compare, select "1 from mytable where parent_id = passId and rowrum", which is more efficient? If you are not interested in the number of records, then there is an EXISTS query one: Select 'y'
Read more

php - multilevel menu with multilevel array -

-
Just ask someone to solve this problem? I want to create a multilevel menu I can not find the right solution generated with multilevel array, it always gets an array_push error My study came from the original idea But still my Can not match the need. This is my MySQL [code] ----- --------------------- --------------- | ID | PARENT_ID | Name | Link | Seq | 1 | 0 | Dashboad | Dashboard / | 1 | 2 | 0 | Menu 1 | Menu 1 / | 2 | 3 | 0 | Menu 2 | Menu 2 / | 3 | 4 | 0 | Menu 3 | Menu 3 / | 4 | 5 | 2 | Joint Add / | 1 | 6 | 3 | Joint Add / | 1 | 7 | 2 | Edit | Edit / | 2 | 8 | 4 | Joint Add / | 1 ------------------------------------------ [/ Code] I want to do something like this in my array array ('dashboard' = & gt; array ('id' = & gt; '' 'Dame' = & gt; 'Dashboard', 'Title' = & gt; 'Dashboard', 'MatchMin' = & gt; Base_URL (). 'Dashboard /', 'Active' => = & Gt; NULL), &
Read more

jQuery UI: Datepicker month format -

-
I am trying to change the format of the month that shows in the popup (not in the date that the picker actually I do not have any choice anywhere to do this, do I like to use a sub-string () or something else? What I normally display is Trying to change: Class = "ui-datepicker-title"> January & lt; / span & gt; ... & lt; / div & gt; Div>
Read more