Perl Monk, Perl Meditation PerlMonks

### Re^8: Array/List Strangeness

by Taulmarill (Deacon)
 on Aug 05, 2009 at 13:29 UTC Need Help??

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.

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
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

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

Create A New User
Domain Nodelet?
Node Status?
node history
Node Type: note [id://786110]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this?Last hourOther CB clients
Other Users?
Others avoiding work at the Monastery: (9)
As of 2024-03-01 10:05 GMT
Voting Booth?
My favourite way to spend a leap day ...

Results (28 votes). Check out past polls.