NAME
BoutrosLab::TSVStream::IOSYNOPSIS
This namespace hierarchy contains roles that allow an object the ability to create a reader (or writer) object that can load (or store) instances of the consuming object class from (or to) a file or stream.
package MyObject;
use Moose;
use MooseX::ClassAttribute;
# the definition of _fields must precede the 'with' statement
class_has '_fields' => (
is => 'ro',
isa => 'ArrayRef',
default => sub { [qw(my_field1 my_field2)] }
);
# one of:
with 'BoutrosLab::TSVStream::IO::Role::Fixed';
# or:
with 'BoutrosLab::TSVStream::IO::Role::Dyn';
has my_field1 => ( isa => 'Int', ... );
has my_field2 => ( isa => 'Str', ... );
package UserCode;
use MyObject;
my $reader = MyObject->reader( file => 'lib/myfobjectfile' );
my $writer = MyObject->writer( file => 'lib/myfobjectfile.over10' );
while (my $obj = $reader->read) {
# $obj is a MyObject
$writer->write($obj) if $obj->my_field1 > 10;
}DESCRIPTION
Consuming classes can acquire the ability to generate reader and writer objects by consuming one of the Roles:
Consuming classes must provide a set of useful attributes, etc. as any normal class. But they also consume one of the roles:
A class that consumes ...::IO::Role::Fixed deals with streams which contain only the fixed defined fields for this class (as specified by the class attribute _class).
A class that consumes ...::IO::Role::Dyn deals with streams which contain the fixed defined fields for this class (as specified by the class attribute _class), but on each line the fixed attributes are followed by a number of dynamic fields.
The stream format is a series of lines.
- .
-
Each line consists of a number of fields, separated by a tab character.
- .
-
If comments are enabled, then lines with the first non-space character being a comment symbol (#) will be discarded on input and not returned by a reader.
- .
-
All non-comment lines must contain the same number of fields.
- .
-
The first line is (usually) a header line that has the field names as the text contents of each field. (The field names are validated on reading to verify match the definition of the object. The header line is not returned by the reader as an object.) A writer will write out a header line unless it was configured not to.
- .
-
The remaining lines of the stream consist of fields that contain data.
- .
-
The first fields contain data for each of the attributes defined by the object (in the order defined by the object). Each field is validated using the type specification for those attributes.
- .
-
For IO::Role::Fixed consuming objects, that must be all of the fields in the stream.
- .
-
For IO::Role::Dyn objects, remaining fields contain text data for additional contents. The number and content of these dynamic fields are determined at run-time - there must be a consistant number of fields throughout an entire stream, but the validity of the content cannot be determined automatically (because each stream can have a different set of dynamic fields, so there is no way for the code to know in advance how to validate them). When reading, if the reader definition did not provide field names for the dynamic fields and if header processing is enabled, then the field names for the dynamic fields will be determined from the input.
Requirements for Comsuning class
The consuming class must satify a number of requirements.
- .
-
class_attribute _fields: must provide a ref to an array of strings that specify the fixed field names.
- .
-
attribute FIELD: each field listed in the _fields class attribute must be defined as an attribute of the consuming object.
Methods Provided to the Consuming class (by either Fixed or Dyn)
reader
The reader method returns an object that reads a stream and produces objects of the consuming class. See BoutrosLab::TSVStream::IO::Reader for details.
writer
The writer method returns an object that writes a stream, from objects of the consuming class (or equivalent values). See BoutrosLab::TSVStream::IO::Writer for details.
Attributes Provided to the Consuming class (only by Dyn)
dyn_fields
the names of the dynamic fields. If they are not provided by the calling code, or by a header (in an input stream), they are set to 'extra1', 'extra2', ...
dyn_values
the values of the dynamic fields (in the same order as dyn_field, and as in a stream).
extra_class_params
List of string values to be passed to the new method for the target object. This can be of value to specific target objects.
The only such attribute defined by this package is install_methods, which is a Boolean attribute that can be provided to a Dyn reader to cause all new objects created by that reader to be provided with accessor methods for the dynamic fields. Generally, this is not needed:
- . the whole point of dynamic fields is that the code doesn't know what the fields will be called
- . it is potentially dangerous since if a dynamic field has the same name as a fixed field or as another dynamic field there would be an attempt to create multiple methods with the same name - this is treated as an error when the dynamic fields are determined
- . it is time-costly both for the cost of installing the methods for each created object dynamically, and also because the target class may not use the Moose make_immuable to pre-compile the object-oriented internal code, since that would prevent adding these attributes
SEE ALSO
- BoutrosLab::TSVStream::IO::Reader
- BoutrosLab::TSVStream::IO::Writer
-
These are the classes of reader and writer objects that are returned by this role. See them for the creation parameters you can provide to the reader and writer methods described here as well as for the methods that reader and writer objects provide.
- BoutrosLab::TSVStream::Format
-
Describes the hierarchy of provided modules that define a set of attributes that are useful to move to/from a text stream.
AUTHOR
John Macdonald - Boutros Lab
ACKNOWLEDGEMENTS
Paul Boutros, Phd, PI - Boutros Lab
The Ontario Institute for Cancer Research