MooseX::Types coercions and $self

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 C开发者_开发知识库lass::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.

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.