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Re^2: Why use references?

by thor (Priest)
on Dec 12, 2005 at 03:06 UTC ( #515944=note: print w/replies, xml ) Need Help??

in reply to Re: Why use references?
in thread Why use references?

Playing devil's advocate, what about arrays and hashes prevents you from returning undef on failure?


The only easy day was yesterday

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Returning undef to indicate error (Re^3: Why use references?)
by jdporter (Canon) on Dec 12, 2005 at 18:58 UTC
    what about arrays and hashes prevents you from returning undef on failure?

    When assigning the result of a function call to an array or reference, the function's return value is evaluated in list context. This means that

    @a = foo(); sub foo { return(undef); }
    makes @a contain a single undef value. How do you know that's supposed to be an error, rather than a non-error single undef?

    Furthermore, in

    %h = foo(); sub foo { return(undef); }
    you get an Odd number of elements in hash assignment warning. Even if you fix/ignore that, how do you know the sub didn't mean to return a (non-error) ( "" => undef ) list?

    If one chooses to use a return value of undef to signify errors, it makes sense to return references for non-error conditions — even for scalars.

    Personally, I try to let any false value indicate failure. This would include undef/''/0 for scalar returns, and empty lists for arrays/hashes. This hash the "advantage" of being consistent with many of the built-in functions.

    But when I need more power (which is usually), I throw exceptions for errors and make the assumption that a function call returning means success.

    eval { my @a = foo(); # if I'm here, then foo() succeeded. at least, it didn't throw an +error. };

    Another thing you sometimes see people do is return data via OUT parameters, and let the function return value only indicate success/failure.

    We're building the house of the future together.

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