Re: More Array Behaviors

[Damian Conway]

Michael Lazzaro wrote:

1) Edge cases in array indexing:

     @a[ undef ]   # undef, or 1?
     @a['foo']     # undef, or 1?

These should generate warnings, at least.
I don't know whether undef or 1 is more correct.

It's certainly a legitimate question. (I'm not sure that @a[undef] == @a[0] is the correct behavior, going forward. It certainly can be error-prone.)

We need an expert decision here, please.

I'd expect that C<undef> converts to zero (with an evitable warning).

I would expect that non-numeric strings like 'foo' convert to C<undef>
and thence on to zero (again with an evitable warning).

Unless C<use strict 'conversions'> is in effect, of course.

Note that converting to and from C<undef> in numeric contexts is much
less troublesome in Perl 6, because the C<//> operator makes it trivial to
catch bad cases and handle them appropriately:

	@a[$str//0]	// silently convert to zero
	@a[$str//die]	// silently convert to exception

What about @a[NaN]?  Just another warning probably.

Actually, I would expect it to throw an exception. Using something that is
explicitly and deliberately *not* a number [*], in a context that expects a number, almost certainly points to a serious problem in the code.

Damian


[*] ...as opposed to 'foo', which is merely implicitly and accidentally not a number ;-)