Re: AW: my int( 1..31 ) $var ?
Christian Renz wrote: Now, I might be stupid, but I keep asking myself what you would need a property for in this example. Yes. It's important to remember that the shiny new hammer of properties is not necessarily the appropriate tool to beat on *every* problem. :-) Damian
AW: my int( 1..31 ) $var ?
It's also far slower. Constructing a 31-element list, junctionizing it, This might well be done at compile-time. And/or, lazily. So the cost of these two steps is likely to be negligible. then testing against each element vs. 2 numeric comparisons. Yes. That's a significant cost in this case. My example was bad. I intended something with more behind it. print creditcard if $var == CreditCard( 'VISA' ); wich should do a mod10 on $var and then match a regex or something. I think one could say CreditCard( 'VISA' ) is then the property. And after reading further seeing it could be smart matched like: print creditcard if $var ~~ CreditCard( 'VISA' ); Brought to a point: Properties could be also smart matched. Murat
AW: my int( 1..31 ) $var ?
my $var = 0; # or my $var = 0; # or my int $var = 0; # or my num $var = 0; # all 4 cases should print is integer print is integer if int $var == $var; This should work as a more generic method to test Integer *value*, rather than type, which IMHO is more useful (and more commonly wanted). I agree. And i found an interesting thread about that in comp.object http://groups.google.de/groups?hl=delr=ie=UTF-8oe=UTF-8threadm=1990S ep28.181057.16740%40odi.comrnum=5prev=/groups%3Fq%3DVariable%2BTypes%2 BVs%2BValue%2BTypes%26hl%3Dde%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26selm%3 D1990Sep28.181057.16740%2540odi.com%26rnum%3D5 Murat
Re: AW: my int( 1..31 ) $var ?
On Sat, 4 Jan 2003, Murat Ünalan wrote: print creditcard if $var == CreditCard( 'VISA' ); wich should do a mod10 on $var and then match a regex or something. I think one could say CreditCard( 'VISA' ) is then the property. And after reading further seeing it could be smart matched like: print creditcard if $var ~~ CreditCard( 'VISA' ); Brought to a point: Properties could be also smart matched. Wouldn't it be easier to say: print creditcard if CreditCard( $var ) eq 'VISA'; ~ John Williams
Re: AW: my int( 1..31 ) $var ?
Murat Ünalan wrote:
print creditcard if $var ~~ CreditCard( 'VISA' );
Brought to a point: Properties could be also smart matched.
Properties *can* be smart-matched:
print creditcard if $var.prop().{CreditCard} ~~ 'VISA';
or:
print creditcard if $var.prop{CreditCard} ~~ 'VISA';
or:
print creditcard if $var.CreditCard ~~ 'VISA';
Damian
AW: my int( 1..31 ) $var ?
Why should you care? Perl 6 isn't going to be that strictly typed, is it? Not even optional ? Murat
Re: AW: AW: my int( 1..31 ) $var ?
On Sun, 5 Jan 2003, Murat Ünalan wrote:
Properties *can* be smart-matched:
print creditcard if $var.prop().{CreditCard} ~~ 'VISA';
or:
print creditcard if $var.prop{CreditCard} ~~ 'VISA';
or:
print creditcard if $var.CreditCard ~~ 'VISA';
I think this is similar to John Williams suggestion:
print creditcard if CreditCard( $var ) eq 'VISA';
Well, no. In my suggestion, CreditCard is a sub which checks whether $var
is a valid credit card, returning the card type.
In Damian's example, he is assuming $var already has a property assigned
to it called CreditCard possibly containing the value 'VISA'. So his has
less processing they either of ours.
The problem I see with:
print creditcard if $var ~~ CreditCard( 'VISA' );
is that CreditCard does not know what $var is. Even if you overload the
smartmatch operator on $var's class, it is still comparing $var with the
value returned from CreditCard.
sub CreditCard
{
#connect to a specific database (VISA, MASTERCARD, ..)
#compare with non-blocked or valid cards
}
...
Excerpt: My concept is to have a twofold view about properties. One
thing that is attributing a type during decleration, and something that
could verified against in other context. All my thinking on that
orginates from Damians Attribute::Type.
Hopefully i do not confuse you too much.
A sub is not a property. It might be a method, which could sometimes look
like a property (as in Damian's third example), but you have strayed so
far away from properties that you are talking about something else now.
~ John Williams
Re: AW: my int( 1..31 ) $var ?
Now, I might be stupid, but I keep asking myself what you would need a
property for in this example. To me, it totally confuses the
underlying structure. When was the last time you asked an integer to
identify itself as a valid credit card number?
It is _not_ a property of the integer that it is a valid cc number,
rather it happens that it will be accepted as valid _by a certain
authority_. So why not go and ask the authority? Compare the case to a
phone number -- the phone number itself doesn't know if its valid. You
could only check a certain format (if e.g. in the USA, in Germany,
that would be very hard). To check the validity, query a directory
server or ask a phone to dial the number. Don't check the number
itself.
To provide even stronger evidence against using properties, consider
the fact that a credit card number will only be accepted with an
expiration date and -- with good merchants -- the three or four-digit
security code on the back of the card. Now you're up to doing
something like
# funky syntax ahead
my $cc = [ num = 8765 4321, expdate = 0799, code = 123 ];
# do magic
# ...
print I'm rich! if $cc.prop{CreditCard(CAMELCARD)};
Ouch! I may be conservative, but again I think you should go and ask
the authority (ie., a validation service). The authority in this case
probably is already encapsulated in a CPAN module and could look like
this:
use CreditCard::Validation;
deduct(10_000_000) if validate($number, $expdate, PERLIAN EXPRESS);
or something like
use CreditCard::Validation qw(ISA CAMELCARD MONKSCLUB);
deduct(10_000_000) if validate($number, $expdate, $bankcode);
depending on your tastes. Yep, it doesn't use funky perl 6 syntax, but
it SWIMs (Says What I Mean, ie. it is readable).
Greetings,
Christian
--
[EMAIL PROTECTED] - http://www.web42.com/crenz/ - http://www.web42.com/
If God were a Kantian, who would not have us till we came to Him from
the purest and best motives, who could be saved?
-- C.S. Lewis, The Problem of Pain
