cdlvj has asked for the wisdom of the Perl Monks concerning the following question:

How do you return a Hash from a perl dll created by perl Ctrl? Been using dlls for months in production, return of a numeric or text works fine. TypeLib Snippet 
    Methods => {
        'New' => {                        RetType => VT_DISPATCH,
        TotalParams => 1,
        NumOptionalParams => 0,
        ParamList => [
                cm    => VT_DISPATCH ]
                },
        'readDirectory' => {RetType => VT_VARIANT,
                              TotalParams => 1,
                    NumOptionalParams => 0,
                    ParamList => [                        dir => VT_BS
+TR ]
                },
                
},  # end of 'Methods'

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snippet of dll code. 
sub readDirectory
{
 my $self = shift;
 my %rlist;
 $rlist{"file1"} = '1';
 $rlist{"file1"} = '2';
 return \%rlist;
}

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Calling program $Lista returns "Win32::OLE" 
 my $Lista = $obj->readDirectory("txt");
    %List = %$Lista; ???????????????????????????

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Replies are listed 'Best First'.
Re: Return hash from a com object. ?
by kcott (Archbishop) on Jun 11, 2016 at 05:00 UTC

    G'day cdlvj,

    Disclaimer: I can't help you with specifics of "perl dll created by perl Ctrl"; sounds like a MSWin thing (with which I'm unfamiliar).

    In many functions, you'll only be interested in the hash's keys and values; the name of &readDirectory suggests it would fall into this category. In these cases, your best choice will probably be: 

    return { %rlist };

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    • There are no references to %rlist when it goes out of scope at the end of &readDirectory: cleanup can occur.
    • All callers have a hash which is decoupled from all other callers' hashes and the original %rlist.

    In other functions, particularly those that need to modify the hash in some way, a reference to the original hash may be important. In these cases, your best choice will probably be: 

    return \%rlist;

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    • There is one reference to %rlist when it goes out of scope at the end of &readDirectory: cleanup cannot occur.
    • All callers have a reference to the same hash; any of which could be modifying the hash in some way, at any time, without notice.

    See also: perlreftut, perldsc and perlref.

    — Ken

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Re: Return hash from a com object. ?
by Anonymous Monk on Jun 11, 2016 at 01:21 UTC
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