MooseX ::类型强制和$ self

Question

Is there anyway to get $self into a MooseX::Types coercion? I have other data in the object that I want to use to seed my coercion from a String to an Object . Alternatively, is there anything like Class::MOP 's initializer that will permit me to do this -- it would have to fire before the type checks.

Requested pseudo code:

with 'DBHandle';
has 'database' => ( isa => 'Str', is => 'ro', default => 'Db' );
has 'schema' => ( isa => 'Str', is => 'ro', default => 'schema' );
has 'table' => ( isa => 'Str', is => 'ro', default => 'column );

has 'columns' => ( isa => DBCols, is => 'ro', default => sub {[qw/foo bar baz/]} );

Here, I want "columns" to coerce to a DBCols -- an ArrayRef of DBCol's (objects) -- requiring the use of catalog , schema , and col attributes found in the class, and with a dbh/singleton provided by DBHandle .

To make this less-pseudo, the actually situation is only slightly more complex. I was able to accomplish the above with around , now what I want I to do is create an attribute trait that would permit this syntax:

has 'column_id' => (
  isa => Int
  , is => 'ro'
  , traits => ['DBKey']
  , default => 5
  , column => 'foo'
);

Where the attribute trait column provided by DBKey , coerces to DBCol the same way that the above columns would: this would require the ability to access the classes database , schema , table , and again the singleton for the dbh .

Answer 1

No. It'd be nice, but coercions are really designed to be global, and no one has written a "context-sensitive coercion" yet, because no one's really sure how to. (Actually, s/coercions/type constraints/ -- it'd be useful just to say "this Str must be a valid column name, defined as an entry in this object's columns HashRef".)

People usually solve this problem with around and/or some combination of BUILD and BUILDARGS .