Re^8: Array/List Strangeness

in reply to Re^7: Array/List Strangeness
in thread Array/List Strangeness

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.

Comment on Re^8: Array/List Strangeness

Replies are listed 'Best First'.
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]

Replies are listed 'Best First'.

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]

In Section Seekers of Perl Wisdom