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Re: lvalue considered harmful...

by BrowserUk (Pope)
on Dec 14, 2002 at 19:54 UTC ( #219886=note: print w/ replies, xml ) Need Help??


in reply to lvalue considered harmful...
in thread Tutorial: Introduction to Object-Oriented Programming

Agreed.

Though I would argue that the problem is not the concept of lvalue subs that is at fault, but just the current implementation.

As they stand currently, they are almost completly useless. The fact that there is no way to access the value being assigned prior to it's assignment, and that any attempt to check it after assignment prevents the assignment, is simply bewildering.

Why the value is not made available to the sub as the last value in @_ I simply don't understand. The current implementation where the assigned value magically overwrites the last available lvalue in the sub if there is one and breaks if there isn't is just simply broken.

Shame. No wonder nobody uses them.


Examine what is said, not who speaks.


Comment on Re: lvalue considered harmful...
Re^2: lvalue considered harmful...
by adrianh (Chancellor) on Dec 14, 2002 at 20:58 UTC

    One of my favourite languages, Pop-11, does it in quite a nice way. You define a separate subroutine for the lvalue side - known as an updater.

    For example, a function to access and update the second element of a linked list can be written in Pop-11 like this:

    define second(list); hd(tl(list)) enddefine; define updaterof second(value, list); value -> hd(tl(list)) enddefine; vars list; [a b c d] -> list; second(list) => ** b 42 -> second(list); second(list) => ** 42 list => ** [a 42 c d]

    All the advantages of writing separate setter/getter functions without the noise (as I see it) in the function names.

    In Pop-11 lvalues are poorly named, since they appear on the right! Doing value -> something in Pop-11 is the same as something = value in perl.

    I find it reads well (something goes into something else) and it also solves that whole "confusing = with ==" problem.

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