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Postings from August 2012
On Fri, 24 Aug 2012, Damian Conway wrote: > > Hugo wrote: > > > This is the bit I'm really not convinced about. I feel there is > > a significant difference between the language that has this: > > my($value) = ($line =~ /value=(\d+)/); # yay, we got a number > > > > and the one that has this: > > my($value) = ($line =~ /value=(\d+)/); # yay, we got a number > > $value += 0; # RT#314159: oops, *now* we got a number > > > > The first of these expresses much that to me seems intrinsic to what > > perl is. The second seems to throw out the DWIM with the bathwater. > > No-one (I hope!) is proposing that Perl's auto-coercions be eliminated, > or modified in any way. Perish the thought! [... a lot of text explaining how auto-coercion may lose the original type ...] I don't understand how this applies to Hugo's example above. You are arguing that Perl variables should be either a number or a string. Hugo is saying that they are both at the same time, until you use them as one or the other. Think of it a little bit like wave- particle duality: a photon doesn't start out as a particle or wave. It exists as both, until an observation forces it to be one or the other. To get back on topic, and Hugo's example: my($value) = ($line =~ /value=(\d+)/); # yay, we got a number So should $value be "originally" a string or a number? Having to decide this before $value is used in an operation is the part that doesn't really fit into Perl 5. > If the original caching mechanism had been implemented so that > autocoercions installed (say) a PVplusIV (for a string with cached > integer autocoercion) or an IVplusPV (for an integer with cached > string autocoercion), then we would have no problem. Smartmatch would > be able to tell what was "really" in the variable, and what was merely > a cached optimization for repeated autocoercions. So how would Hugo's example work with this "fixed" type system? How would it know that it has to treat $value as a number? <kidding>By storing capture groups that only contain \d+ as SvIV?</kidding> I maintain that we would still have a problem even if autocoercions were changed in the way you describe. Cheers, -JanThread Previous | Thread Next