| Subject: | Simpler validation of data values during init and "set_" |
When creating a new object, there is no way to assess the validity
of argument values, without having to create your own BUILD() and
set_ methods:
package File::Heirarchy;
use Class::Std;
{
my %root_of :ATTR( init_arg => root );
# etc...
}
my $tree = eval { File::Heirarchy->new({ root => '' }) }; # Error!
In this instance, I want the call to new() to fail, though Class::Std
is quite happy to allow it, on account of the value being defined.
Doing a custom BUILD() and set_ function "works", but it seems to
go against the principle espoused in PBP to have automatic attribute
initialization and verification. It also opens the door to "rewriting"
that code poorly.
In addition, there are also some other problems with doing additional
checking in a custom BUILD() function (see bug #18747).
What I'd *really* like to do is write a function that does those extra
checks, and provide it as an ATTR() argument:
package File::Heirarchy;
use Class::Std;
{
my %root_of :ATTR( init_arg => root, validator => 'check_root' );
# Additional verification for root argument.
sub check_root {
my ($self, $root) = @_;
croak "'root' must be non-empty" unless length $root;
croak "'root' must be an existing directory" unless -d $root;
return 1;
}
# etc...
}
This way, I get the automatic attribute initialization and verification,
plus my additional checks, without having to write any extra functions.
Attached is the module with the necessary changes (from v0.0.8) to
implement this. I believe the changes also fix bug #18747.
| Subject: | Std.pm |
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