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Re: undef'ing @arrays caveat

by Kanji (Parson)
on Apr 20, 2002 at 00:40 UTC ( #160712=note: print w/replies, xml ) Need Help??

in reply to undef'ing @arrays caveat

Since undef is a perfectly valid value for an element of an array, what your doing is no different than @array = ( undef ); sans the parens.

Also, while @array = () may do what you want, @array is still defined; it just evaluates as false when you test for truth (which you were).

To truly undefine @array you'd want to use undef @array; instead.


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Re: Re: undef'ing @arrays caveat
by dmmiller2k (Chaplain) on Apr 20, 2002 at 22:46 UTC

    Actually, arrays cannot be undefined, just made empty (same with hashes). If you try undef @array in the debugger and then dump its value using the 'x' command, the effect is the same as if you had said @array = (), namely 'empty array'. (The same may be said for hashes, which under the above circumstances, produce the message, 'empty hash').

    Only scalars may be truly undefined; undef is itself merely a value, albeit a special one. As a C/C++ programmer, I rather think of scalars analagous to pointers -- sort of "auto-allocating, auto-dereferencing, type-ambivalent pointers", but pointers nonetheless, with undef rather analagous to NULL.


    If you GIVE a man a fish you feed him for a day
    TEACH him to fish and you feed him for a lifetime

      I was thinking of definedness in the defined sense, but after some testing I discovered something really bizarre:

      Calling defined on an array that was declared as empty versus one that had been populated and then later emptied returns different results!

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