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Postings from July 2013
On Wed Jul 31 02:42:52 2013, zefram@fysh.org wrote: > Father Chrysostomos via RT wrote: > >If $a+$b returns a value, not a variable, then we could say that \ and > >for(...) and func(...) impose "variable context". > > The usual term for this is "lvalue context". A variable (that can vary) > is an lvalue. A read-only scalar is also an lvalue. > > It is instructive to compare against C. The C equivalent of Perl's \ > operator is &. C's & operator requires that the operand be an lvalue > (but not necessarily mutable), and it is a compile-time error to apply > it to a non-lvalue. Perl's pass-by-reference semantics would conflict > with any attempt to prevent enreferencement of non-lvalues. > > Are you going to document \'s variable-generating semantics? I’m not sure how to go about that, nor do I think it is necessary. I always assumed that $a+$b would return a new mutable scalar, and that \($a+$b) just references a scalar that would otherwise have been short-lived. Nothing in the observable behaviour contradicts that view. This bare value vs variable distinction is not something that is mentioned anywhere in the Perl documentation. Is it something we want to document rigidly, or will it just add to the mental burden? Most of the time it makes no difference. In we want to put it anywhere, it should go under the documentation for constants, wherever that might be, since that is where it actually matters. Apparently we don’t define the term ‘constant’ clearly anywhere. One thing that makes this difficult is that constants are currently inconsistent. Making constants created by overload::constant and constant.pm consistently return read-only scalars broke CPAN modules. At this stage, I am willing to leave things inconsistent, as the changes I have made so far have allowed me to fix the bugs I wanted to fix. -- Father Chrysostomos --- via perlbug: queue: perl5 status: open https://rt.perl.org:443/rt3/Ticket/Display.html?id=109744Thread Previous | Thread Next