Re: [MacPerl] Location of MAIN code relative to subroutines

[Ero Brown <ero@fiber.net>]

Right you are Charles!

Thank you for your post . . . some quick tests confirmed
what you said.

I _really_ dislike the fact that the scope of "my" vars
is dependent upon whether or not they are placed before
or after the subroutines.

I would think that this behavior makes a good argument for
placing all of your "MAIN" code _after_ all subs as another
check to help ensure you aren't accidentally using "my" vars
improperly.  (Of course, if you want to count on their
"global" behavior, it doesn't matter, but I think some care
must then be taken to make sure scope issues are clear.)

Anyway, I've been able to fix my code.  Thank you for
elucidating my understanding Charles (and Paul).

Ero

----------------------------------------------------------------

>In the code you posted, the use of the variables $inputfile and
>$TIME_OFFSET *within* the subroutine definitions refer to the
>*package* (or "global," if you will) variables $main::inputfile
>and $main::TIME_OFFSET.  As such, any changes you make to one
>of the package variables in the subroutine will be seen by
>the other.
>
>However, in the main part of your routine, you also define two
>*lexically-scoped* variables $TIME_OFFSET and $inputFile, which,
>as Paul noted, have nothing to do with the package variables and
>only exist within that lexical scope.
>
>In the case of $TIME_OFFSET, you assigned a value to the lexically-
>scoped variable and tried to read from the package value and
>failed to get anything.  In the case of $inputFile, however,
>all interaction is within subroutines and hence involving the
>package variable.  The lexical variable "$inputFile", though
>defined, is never used within its lexical scope.
>
>If, however, the "my" statements are placed before the
>subroutine blocks, then those blocks are within the lexical
>scope of the my statements, and the routines will use
>the lexical variables and not package variables.
>
>A recent article in TPJ goes into a fair amount of detail on the
>differences between lexical and package variables.
>
>HTH,
>
>-C
>
>At 1:05 PM -0600 4/27/1999, Ero Brown wrote:
>>Thanks for your reply Paul.
>>
>>So how does the $inputfile variable escape the same fate
>>as the $TIME_OFFSET variable?  Given the definition of "my"
>>variables you provided from perlsub, wouldn't the value of
>>the $inputfile in the "ParseFile" sub be in question as well?
>>
>>Ero Brown
>>
>>-------------------------------------------------------------
>>
>>
>>>On Tue, Apr 27, 1999 at 11:41:32AM -0600, Ero Brown wrote:
>>>}
>>>} I seem to ben having a problem regarding the placement of "MAIN"
>>>} code relative to subroutines.
>>>}
>>>} When I execute the following script, the variable $TIME_OFFSET
>>>} doesn't seem to have value in the "ParseFile" subroutine.
>>>}
>>>} However, if I move the location of my "MAIN" code (or actually
>>>} just the code snip in "MAIN" where $TIME_OFFSET is defined) to
>>>} a position before my subroutines, this script appears to work
>>>} correctly.
>>>}
>>>} Is this a MacPerl bug, or am I missing something here?
>>>} I'm currently using MacPerl 5.2.0r4.
>>>
>>>You're missing something.  From perlsub (I don't remember what Shuck
>>>calls it):
>>>
>>>
>>>     Unlike dynamic variables created by the "local" operator,
>>>     lexical variables declared with "my" are totally hidden from
>>>     the outside world, including any called subroutines (even if
>>>     it's the same subroutine called from itself or elsewhere--
>>>     every call gets its own copy).
>>>
>>>$TIME_OFFSET only exists from the point you declare it to the end of
>>>the file.  The subroutines never see it.
>>>
>>>
>>>}
>>>} Thanks,
>>>}
>>>} Ero Brown
>>>}
>>>
>>>--
>>>Paul Schinder
>>>schinder@pobox.com
>>
>>
>>
>>
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