if ( @x ) {
  $x[-1]->meth();
}
else {
   die "no elements in \@x\n"; # r whatever
}
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Try this one for size:

perl -e '$x[-1] = 0;'
__OUTPUT__
Modification of non-creatable array value attempted, subscript -1 at -
+e line 1.
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It would appear that you cannot autovivify an array element by counting backward from the last element using negative subscripts. Likewise, this will throw the same error:

perl -e '@x = ( 1, 2, 3 ); $x[-4] = 0;'
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Again, this is attempting to autovivify an element prior to the first element ($x[0]) by using a negative index that will count backward past the beginning of the array.

I don't consider the fact that you can't do this to be a bug, if ever there were a feature, this is it. ;)

Update: After reading your update, I just wanted to comment: I really think that the problem is two-fold: First, you're attempting to autovivify by indexing backwards from an array that has no elements (so there is no concept of the last element). The second problem is that even if the array has elements (thus creating a concept of 'last element'), attempting to index to the left of the first element (ie, before $x[0]) is another impossibility; you can't autovivify an element prior to the first element of an array. In an array that contains no elements, you're breaking both rules; you're attempting to count backward from the last element, when there is no last element. And since there is no last element, any element you autovivify by counting backwards will have to come before the nonexistant first element. It's madness.

Addressing your update: Right, I got most of that on my own and thats basically what I was attempting to convery in my update. Now I just think the error message sucks =]

As a general rule, perl error messages try to be as short as possible while still conveying all of the neccessary info that sets *this* type of error apart from *that* type of error.

The main motivation for this (as i understand it) is to keep them short for people who allready understand the various classes of problems, and just need a quick pointer to the line number and the type of think they screwed up.

If/when people are confused by perl error messages, they should ALWAYS consult perldiag, or use diagnostics

laptop:~> perl -Mdiagnostics -e 'my @x; $x[-1]->meth'
Modification of non-creatable array value attempted, subscript -1 at -
+e line 1 (#1)
    (F) You tried to make an array value spring into existence, and th
+e
    subscript was probably negative, even counting from end of the arr
+ay
    backwards.
    
Uncaught exception from user code:
        Modification of non-creatable array value attempted, subscript
+ -1 at -e line 1.
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Yes, buy why does doing ->meth involve a modification or a creation of the left hand side?

I started to write this...

It doesn't. perl can't even make it that far because it can't figure out what it is you are trying to call "meth" on. Before it ever even gets arround to trying, it has to "make an array value spring into existence" and when it tried, it found that "subscript -1" ment "the subscript was (probably) negative" so ultimately you were asking it to set (aka: modify) a "non-creatable array value"

...but then i started to see your point: "Modification" ? why is refrencing the (non-creatable) array value to call a method on it considered a modification?

It would make more sense to say something like "Reference of non-creatable array value attempted"...

laptop:~> perl -e '$y = \$x[-1000];'
Modification of non-creatable array value attempted, subscript -1000 a
+t -e line 1.
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