he scalar is having its reference count dropped twice -- once when you leave the XS function, and once when @_ is cleaned up after that function returns.

Thankyou. That was the bit I was not getting.

The reason for wanting to handle the case of readonly inputs is that I cannot guarentee that the caller (should this ever get into the wild), won't pass a constant that becomes the first parameter.

The reason for wanting to return the argument is the same reason that I can do

print $scalar1 .= $scalar2;
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I hate modules that force me to do

my $arg = 1;
someMutator( $arg );
print $arg;
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Instead of

print someMutator( 1 );
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Try using Tk if its methods did not return the object:

my $widget = Tk::SomeWidget->new( ... );
$widget->Add( ... );
$widget->pack( ... );
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Instead of

my $widget = Tk::SomeWidget->new( 
    ... 
)->Add(
   ...
)->pack( ... );
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So, now I understand why the increment is necessary, can you clarify what is wrong (technically rather than preference), with doing an increment to counter one of the decrements?