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
• Boolification is overloaded to always return true.
• Coderefification is overloaded to call "coerce".
• 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:
• 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.
• 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
<https://github.com/tobyink/p5-type-tiny/issues>.
SEE ALSO
Type::Tiny::Manual.
Type::Tiny, Type::Library, Type::Utils, Types::Standard.
Type::Coercion::Union.
Moose::Meta::TypeCoercion.
AUTHOR
Toby Inkster <tobyink@cpan.org>.
COPYRIGHT AND LICENCE
This software is copyright (c) 2013-2014, 2017-2023 by Toby Inkster.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
DISCLAIMER OF WARRANTIES
THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
perl v5.36.0 2023-02-01 Type::Coercion(3pm)
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