Re: non fixed number of properties in constructor
I almost got the ideas with all your replies, thanks.
On 7/20/06, D. Bolliger [EMAIL PROTECTED] wrote:
Hi Ken
Ken Perl am Mittwoch, 19. Juli 2006 12:04:
ok, let me explain what I mean.
Better done by inline/bottom posting, if you already got a bottom answer :-)
$account = new Account;
then I can get the currency of the two countries,
$account-currency_us;
$account-currency_fr;
after I freeze the code, a new country jumps out, suppose i need
support Iraq, but now I can't use this,
$account-currency_iraq;
If I want to support this method, I have to modify the constructor
again to add the new country, but what I am looking for is the
solution that doesn't need to modify the constructor again.
If I don't misunderstand you, you are looking for a lookup class to find out
the currency of countries, and the (country, currency) pairs are defined in a
database.
You have two variables here:
1) the number of (country, currency) pairs
2) the information needed to access the underlying database table
sub new {
my $class=shift;
my $dbh=shift; # of DBI class
my ($tablename, @fieldnames)[EMAIL PROTECTED] # if this flexibility needed
my %pairs;
# initialize %pairs (country, currency) from database
return bless \%pairs, $class;
}
sub currency {
my ($self, $country)[EMAIL PROTECTED];
return exists $self-{$country}
? $self-{$country}
: undef;
}
The usage of this class is not easy because of the many arguments to new().
But it's enough flexible as to not need changes.
For easier usage, you could derive a class that encapsulates most or all
arguments to new() of the base class (by hardcoding it, by using a
configfile).
But I'm a bit in doubt as to whether there is not a simpler solution...
Maybe this gives you an idea?
And sorry for my bad english :-)
Dani
[history]
On 7/19/06, Rob Dixon [EMAIL PROTECTED] wrote:
Ken Perl wrote:
I find a difficulty when writing the constructor which may has dynamic
and non fixed number of properties, say we want to construct a new
class Account,
package Account;
sub new {
my $class = shift;
my $self = { currency_us=undef,
currency_fr =undef,
};
bless $self, $class;
return $self;
}
If we want to create new object with more other contries' currency and
don't want to modify the code, for example, get more other contries'
name from database, how to write my constructor method and it can live
with the dynamic database?
I'm unclear what you want. I don't see how you an do anything without
modifying the code. Do you mean you want to subclass Account?
Suppose you have a list of currencies in @currencies (I can't explain how
to get it there as I don't know where it's coming from) you can add these
to your object with:
my @currencies = qw/ currency_uk currency_gr currency_sp /;
@[EMAIL PROTECTED] = ();
Does this help at all?
Rob
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Re: non fixed number of properties in constructor
Ken Perl wrote:
I find a difficulty when writing the constructor which may has dynamic
and non fixed number of properties, say we want to construct a new
class Account,
package Account;
sub new {
my $class = shift;
my $self = { currency_us=undef,
currency_fr =undef,
};
bless $self, $class;
return $self;
}
If we want to create new object with more other contries' currency and
don't want to modify the code, for example, get more other contries'
name from database, how to write my constructor method and it can live
with the dynamic database?
I'm unclear what you want. I don't see how you an do anything without modifying
the code. Do you mean you want to subclass Account?
Suppose you have a list of currencies in @currencies (I can't explain how to get
it there as I don't know where it's coming from) you can add these to your
object with:
my @currencies = qw/ currency_uk currency_gr currency_sp /;
@[EMAIL PROTECTED] = ();
Does this help at all?
Rob
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/ http://learn.perl.org/first-response
Re: non fixed number of properties in constructor
ok, let me explain what I mean.
$account = new Account;
then I can get the currency of the two countries,
$account-currency_us;
$account-currency_fr;
after I freeze the code, a new country jumps out, suppose i need
support Iraq, but now I can't use this,
$account-currency_iraq;
If I want to support this method, I have to modify the constructor
again to add the new country, but what I am looking for is the
solution that doesn't need to modify the constructor again.
On 7/19/06, Rob Dixon [EMAIL PROTECTED] wrote:
Ken Perl wrote:
I find a difficulty when writing the constructor which may has dynamic
and non fixed number of properties, say we want to construct a new
class Account,
package Account;
sub new {
my $class = shift;
my $self = { currency_us=undef,
currency_fr =undef,
};
bless $self, $class;
return $self;
}
If we want to create new object with more other contries' currency and
don't want to modify the code, for example, get more other contries'
name from database, how to write my constructor method and it can live
with the dynamic database?
I'm unclear what you want. I don't see how you an do anything without modifying
the code. Do you mean you want to subclass Account?
Suppose you have a list of currencies in @currencies (I can't explain how to get
it there as I don't know where it's coming from) you can add these to your
object with:
my @currencies = qw/ currency_uk currency_gr currency_sp /;
@[EMAIL PROTECTED] = ();
Does this help at all?
Rob
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Re: non fixed number of properties in constructor
On 07/19/2006 05:04 AM, Ken Perl wrote:
ok, let me explain what I mean.
$account = new Account;
then I can get the currency of the two countries,
$account-currency_us;
$account-currency_fr;
after I freeze the code, a new country jumps out, suppose i need
support Iraq, but now I can't use this,
$account-currency_iraq;
If I want to support this method, I have to modify the constructor
again to add the new country, but what I am looking for is the
solution that doesn't need to modify the constructor again.
You should install Class::Accessor from CPAN (or your Debian
CD's if you have Debian), and use Class::Accessor as a base
class to your 'Account' class.
Override new so that it calls mk_accessors for all of the keys
in the hash you give to new(). With Class::Accessor, what you
want to do becomes child's play:
#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
my $obj = Person4-new({
height = 4.10,
name = 'John Gateway',
});
print Dumper($obj);
exit;
package Person4;
use base 'Class::Accessor';
sub new {
my ($class, $href) = @_;
my $self = {};
bless ($self, $class);
if ($href) {
my @keys = keys %$href;
__PACKAGE__-mk_accessors(@keys);
$self-$_($href-{$_}) for (@keys);
}
$self;
}
__HTH__
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Re: non fixed number of properties in constructor
Hi Ken
Ken Perl am Mittwoch, 19. Juli 2006 12:04:
ok, let me explain what I mean.
Better done by inline/bottom posting, if you already got a bottom answer :-)
$account = new Account;
then I can get the currency of the two countries,
$account-currency_us;
$account-currency_fr;
after I freeze the code, a new country jumps out, suppose i need
support Iraq, but now I can't use this,
$account-currency_iraq;
If I want to support this method, I have to modify the constructor
again to add the new country, but what I am looking for is the
solution that doesn't need to modify the constructor again.
If I don't misunderstand you, you are looking for a lookup class to find out
the currency of countries, and the (country, currency) pairs are defined in a
database.
You have two variables here:
1) the number of (country, currency) pairs
2) the information needed to access the underlying database table
sub new {
my $class=shift;
my $dbh=shift; # of DBI class
my ($tablename, @fieldnames)[EMAIL PROTECTED] # if this flexibility needed
my %pairs;
# initialize %pairs (country, currency) from database
return bless \%pairs, $class;
}
sub currency {
my ($self, $country)[EMAIL PROTECTED];
return exists $self-{$country}
? $self-{$country}
: undef;
}
The usage of this class is not easy because of the many arguments to new().
But it's enough flexible as to not need changes.
For easier usage, you could derive a class that encapsulates most or all
arguments to new() of the base class (by hardcoding it, by using a
configfile).
But I'm a bit in doubt as to whether there is not a simpler solution...
Maybe this gives you an idea?
And sorry for my bad english :-)
Dani
[history]
On 7/19/06, Rob Dixon [EMAIL PROTECTED] wrote:
Ken Perl wrote:
I find a difficulty when writing the constructor which may has dynamic
and non fixed number of properties, say we want to construct a new
class Account,
package Account;
sub new {
my $class = shift;
my $self = { currency_us=undef,
currency_fr =undef,
};
bless $self, $class;
return $self;
}
If we want to create new object with more other contries' currency and
don't want to modify the code, for example, get more other contries'
name from database, how to write my constructor method and it can live
with the dynamic database?
I'm unclear what you want. I don't see how you an do anything without
modifying the code. Do you mean you want to subclass Account?
Suppose you have a list of currencies in @currencies (I can't explain how
to get it there as I don't know where it's coming from) you can add these
to your object with:
my @currencies = qw/ currency_uk currency_gr currency_sp /;
@[EMAIL PROTECTED] = ();
Does this help at all?
Rob
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