Type::Coercion(3pm) - phpMan

Type::Coercion(3pm) User Contributed Perl Documentation Type::Coercion(3pm)

NAME
Type::Coercion - a set of coercions to a particular target type constraint

STATUS
This module is covered by the Type-Tiny stability policy.

DESCRIPTION
Constructors
"new(%attributes)"
Moose-style constructor function.

"add($c1, $c2)"
Create a Type::Coercion from two existing Type::Coercion objects.

Attributes
Attributes are named values that may be passed to the constructor. For each attribute,
there is a corresponding reader method. For example:

my $c = Type::Coercion->new( type_constraint => Int );
my $t = $c->type_constraint; # Int

Important attributes

These are the attributes you are likely to be most interested in providing when creating
your own type coercions, and most interested in reading when dealing with coercion
objects.

"type_constraint"
Weak reference to the target type constraint (i.e. the type constraint which the
output of coercion coderefs is expected to conform to).

"type_coercion_map"
Arrayref of source-type/code pairs.

"frozen"
Boolean; default false. A frozen coercion cannot have "add_type_coercions" called upon
it.

"name"
A name for the coercion. These need to conform to certain naming rules (they must
begin with an uppercase letter and continue using only letters, digits 0-9 and
underscores).

Optional; if not supplied will be an anonymous coercion.

"display_name"
A name to display for the coercion when stringified. These don't have to conform to
any naming rules. Optional; a default name will be calculated from the "name".

"library"
The package name of the type library this coercion is associated with. Optional.
Informational only: setting this attribute does not install the coercion into the
package.

Attributes related to parameterizable and parameterized coercions

The following attributes are used for parameterized coercions, but are not fully
documented because they may change in the near future:

"coercion_generator"
"parameters"
"parameterized_from"

Lazy generated attributes

The following attributes should not be usually passed to the constructor; unless you're
doing something especially unusual, you should rely on the default lazily-built return
values.

"compiled_coercion"
Coderef to coerce a value ($_[0]).

The general point of this attribute is that you should not set it, but rely on the
lazily-built default. Type::Coerce will usually generate a pretty fast coderef,
inlining all type constraint checks, etc.

"moose_coercion"
A Moose::Meta::TypeCoercion object equivalent to this one. Don't set this manually;
rely on the default built one.

Methods
Predicate methods

These methods return booleans indicating information about the coercion. They are each
tightly associated with a particular attribute. (See "Attributes".)

"has_type_constraint", "has_library"
Simple Moose-style predicate methods indicating the presence or absence of an
attribute.

"is_anon"
Returns true iff the coercion does not have a "name".

The following predicates are used for parameterized coercions, but are not fully
documented because they may change in the near future:

"has_coercion_generator"
"has_parameters"
"is_parameterizable"
"is_parameterized"

Coercion

The following methods are used for coercing values to a type constraint:

"coerce($value)"
Coerce the value to the target type.

Returns the coerced value, or the original value if no coercion was possible.

"assert_coerce($value)"
Coerce the value to the target type, and throw an exception if the result does not
validate against the target type constraint.

Returns the coerced value.

Coercion code definition methods

These methods all return $self so are suitable for chaining.

"add_type_coercions($type1, $code1, ...)"
Takes one or more pairs of Type::Tiny constraints and coercion code, creating an
ordered list of source types and coercion codes.

Coercion codes can be expressed as either a string of Perl code (this includes objects
which overload stringification), or a coderef (or object that overloads
coderefification). In either case, the value to be coerced is $_.

"add_type_coercions($coercion_object)" also works, and can be used to copy coercions
from another type constraint:

$type->coercion->add_type_coercions($othertype->coercion)->freeze;

"freeze"
Sets the "frozen" attribute to true. Called automatically by Type::Tiny sometimes.

"i_really_want_to_unfreeze"
If you really want to unfreeze a coercion, call this method.

Don't call this method. It will potentially lead to subtle bugs.

This method is considered unstable; future versions of Type::Tiny may alter its
behaviour (e.g. to throw an exception if it has been detected that unfreezing this
particular coercion will cause bugs).

Parameterization

The following method is used for parameterized coercions, but is not fully documented
because it may change in the near future:

"parameterize(@params)"

Type coercion introspection methods

These methods allow you to determine a coercion's relationship to type constraints:

"has_coercion_for_type($source_type)"
Returns true iff this coercion has a coercion from the source type.

Returns the special string "0 but true" if no coercion should actually be necessary
for this type. (For example, if a coercion coerces to a theoretical "Number" type,
there is probably no coercion necessary for values that already conform to the
"Integer" type.)

"has_coercion_for_value($value)"
Returns true iff the value could be coerced by this coercion.

Returns the special string "0 but true" if no coercion would be actually be necessary
for this value (due to it already meeting the target type constraint).

The "type_constraint" attribute provides a type constraint object for the target type
constraint of the coercion. See "Attributes".

Inlining methods

The following methods are used to generate strings of Perl code which may be pasted into
stringy "eval"uated subs to perform type coercions:

"can_be_inlined"
Returns true iff the coercion can be inlined.

"inline_coercion($varname)"
Much like "inline_coerce" from Type::Tiny.

Other methods

"qualified_name"
For non-anonymous coercions that have a library, returns a qualified
"MyLib::MyCoercion" sort of name. Otherwise, returns the same as "name".

"isa($class)", "can($method)", "AUTOLOAD(@args)"
If Moose is loaded, then the combination of these methods is used to mock a
Moose::Meta::TypeCoercion.

The following methods exist for Moose/Mouse compatibility, but do not do anything useful.

"compile_type_coercion"
"meta"

Overloading
o Boolification is overloaded to always return true.

o Coderefification is overloaded to call "coerce".

o On Perl 5.10.1 and above, smart match is overloaded to call "has_coercion_for_value".

Previous versions of Type::Coercion would overload the "+" operator to call "add". Support
for this was dropped after 0.040.

DIAGNOSTICS
Attempt to add coercion code to a Type::Coercion which has been frozen
Type::Tiny type constraints are designed as immutable objects. Once you've created a
constraint, rather than modifying it you generally create child constraints to do what
you need.

Type::Coercion objects, on the other hand, are mutable. Coercion routines can be added
at any time during the object's lifetime.

Sometimes Type::Tiny needs to freeze a Type::Coercion object to prevent this. In
Moose and Mouse code this is likely to happen as soon as you use a type constraint in
an attribute.

Workarounds:

o Define as many of your coercions as possible within type libraries, not within the
code that uses the type libraries. The type library will be evaluated relatively
early, likely before there is any reason to freeze a coercion.

o If you do need to add coercions to a type within application code outside the type
library, instead create a subtype and add coercions to that. The "plus_coercions"
method provided by Type::Tiny should make this simple.

BUGS
Please report any bugs to <http://rt.cpan.org/Dist/Display.html?Queue=Type-Tiny>.