Re^6: Array/List Strangeness

That's what Taulmarill meant.

Basically: an "empty" array can have any size, but an empty list always has size 0.

UPDATE: that should show it...

  DB<1> @a[3..5]=()
 
  DB<2> @b[3..5]=()
 
  DB<3> print scalar @a
6
  DB<4> print ( () = @a,@b )
 
  DB<5> @c= @a,@b
 
  DB<6> print scalar @c
6
  DB<7> @c=(@a,@b)
 
  DB<8> print scalar @c
12  
  DB<9> print ( () = (@a,@b) )
 
  DB<10> push @a,@b
 
  DB<11> print scalar @a
12
  DB<12> x @a
0  undef
1  undef
2  undef
3  undef
4  undef
5  undef
6  undef
7  undef
8  undef
9  undef
10  undef
11  undef
[download]

Line 12 clearly shows, that concatenating two "empty" arrays leads to a larger "empty" array...

Anyway the difference between line 5 and 7 is somehow surprising ...

UPDATE: Aaaaaargh!!! 8)

In line 5, I fell into the scalar comma operator trap again ... it's basically (@c=@a),(@b)

Cheers Rolf

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Re^7: Array/List Strangeness by jethro (Monsignor) on Aug 05, 2009 at 13:06 UTC
Well, Taulmarill was questioning Ikegamis words 'non-existing array element'. So I'm just pointing out that there is a real difference between non-existing array element and undef'd array element (even if we would wish otherwise to have more consistency). ++ for what you are saying after 'Basically:', an excellent description of the situation	[reply]
Re^8: Array/List Strangeness by Taulmarill (Deacon) on Aug 05, 2009 at 13:29 UTC
I admit that i might have misunderstood something here .... although i'm not sure what.... Could we from now on agree not to talk about (non)existing array elements, but about elements <= $#array and elements > $#array. That might make things easier for my twisted, sleep deprived mind. update: also i'd like $[ to stay 0.	[reply]
Re^9: Array/List Strangeness by LanX (Saint) on Aug 05, 2009 at 16:28 UTC
Could we from now on agree not to talk about (non)existing array elements, Well we have an exists function, why shouldn't we talk about (non)existing array elements? :-) Existence is an an important point to describe the behaviors of slicing, i.e. mostly returning undef for non-existing elements. (And I think what ikegami meant) Let's express it in LRTs (Lanx's Rule of Thumb ;-) `1. Arrayslices (and hashslices) always return values for all requested elements. Not existing elements are represented as 'undef'.` `DB<1> @a=1..2 DB<2> x @a[0,1] 0 1 1 2 DB<3> x @a[0,3] 0 1 1 undef DB<4> x @a[2,3] 0 undef 1 undef DB<5> @a=() DB<6> x @a[1,2] 0 undef 1 undef` [download] `2. Listlices work alike if and only if at least one of the requested elements exists. Otherwise it returns an empty list.` `DB<5> x (1,2)[0,1] 0 1 1 2 DB<6> x (1,2)[0,3] 0 1 1 undef DB<7> x (1,2)[2,3] # DIFFERENT! empty array DB<8> x ()[0..3] # DIFFERENT! empty array DB<9> x (undef,undef)[0,2] 0 undef 1 undef` [download] Note: Maybe the x command in the debugger should better say "empty list" instead of "empty array".... Please correct me if I missed something with this "model" of slice behavior. Cheers Rolf	[reply] [d/l] [select]
Re^8: Array/List Strangeness by LanX (Saint) on Aug 05, 2009 at 16:36 UTC
++ for what you are saying after 'Basically:', an excellent description of the situation Actually it should be defined what "empty" means. `undef` can be an existing element of a list! `DB<1> p scalar ( ()=(undef,undef) ) 2` [download] Cheers Rolf	[reply] [d/l] [select]