Specio::Coercion(3pm) User Contributed Perl DocumentationSpecio::Coercion(3pm)
NAME
Specio::Coercion - A class representing a coercion from one type to
another
VERSION
version 0.48
SYNOPSIS
my $coercion = $type->coercion_from_type('Int');
my $new_value = $coercion->coerce_value(42);
if ( $coercion->can_be_inlined() ) {
my $code = $coercion->inline_coercion('$_[0]');
}
DESCRIPTION
This class represents a coercion from one type to another. Internally,
a coercion is a piece of code that takes a value of one type returns a
new value of a new type. For example, a coercion from c<Num> to "Int"
might round a number to its nearest integer and return that integer.
Coercions can be implemented either as a simple subroutine reference or
as an inline generator subroutine. Using an inline generator is faster
but more complicated.
API
This class provides the following methods.
Specio::Coercion->new( ... )
This method creates a new coercion object. It accepts the following
named parameters:
• from => $type
The type this coercion is from. The type must be an object which
does the Specio::Constraint::Role::Interface interface.
This parameter is required.
• to => $type
The type this coercion is to. The type must be an object which does
the Specio::Constraint::Role::Interface interface.
This parameter is required.
• coercion => sub { ... }
A subroutine reference implementing the coercion. It will be called
as a method on the object and passed a single argument, the value
to coerce.
It should return the new value.
This parameter is mutually exclusive with "inline_generator".
Either this parameter or the "inline_generator" parameter is
required.
You can also pass this option with the key "using" in the parameter
list.
• inline_generator => sub { ... }
This should be a subroutine reference which returns a string
containing a single term. This code should not end in a semicolon.
This code should implement the coercion.
The generator will be called as a method on the coercion with a
single argument. That argument is the name of the variable being
coerced, something like '$_[0]' or '$var'.
This parameter is mutually exclusive with "coercion".
Either this parameter or the "coercion" parameter is required.
You can also pass this option with the key "inline" in the
parameter list.
• inline_environment => {}
This should be a hash reference of variable names (with sigils) and
values for that variable. The values should be references to the
values of the variables.
This environment will be used when compiling the coercion as part
of a subroutine. The named variables will be captured as closures
in the generated subroutine, using Eval::Closure.
It should be very rare to need to set this in the constructor. It's
more likely that a special coercion subclass would need to provide
values that it generates internally.
This parameter defaults to an empty hash reference.
• declared_at => $declared_at
This parameter must be a Specio::DeclaredAt object.
This parameter is required.
$coercion->from(), $coercion->to(), $coercion->declared_at()
These methods are all read-only attribute accessors for the
corresponding attribute.
$coercion->description
This returns a string describing the coercion. This includes the names
of the to and from type and where the coercion was declared, so you end
up with something like 'coercion from Foo to Bar declared in package
My::Lib (lib/My/Lib.pm) at line 42'.
$coercion->coerce($value)
Given a value of the right "from" type, returns a new value of the "to"
type.
This method does not actually check that the types of given or return
values.
$coercion->inline_coercion($var)
Given a variable name like '$_[0]' this returns a string with code for
the coercion.
Note that this method will die if the coercion does not have an inline
generator.
$coercion->can_be_inlined()
This returns true if the coercion has an inline generator and the
constraint it is from can be inlined. This exists primarily for the
benefit of the "inline_coercion_and_check()" method for type constraint
object.
$coercion->inline_environment()
This returns a hash defining the variables that need to be closed over
when inlining the coercion. The keys are full variable names like
'$foo' or '@bar'. The values are references to a variable of the
matching type.
$coercion->clone()
Returns a clone of this object.
$coercion->clone_with_new_to($new_to_type)
This returns a clone of the coercion, replacing the "to" type with a
new one. This is intended for use when the to type itself is being
cloned as part of importing that type. We need to make sure the newly
cloned coercion has the newly cloned type as well.
ROLES
This class does the Specio::Role::Inlinable role.
SUPPORT
Bugs may be submitted at
<https://github.com/houseabsolute/Specio/issues>.
SOURCE
The source code repository for Specio can be found at
<https://github.com/houseabsolute/Specio>.
AUTHOR
Dave Rolsky <autarch@urth.org>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2012 - 2022 by Dave Rolsky.
This is free software, licensed under:
The Artistic License 2.0 (GPL Compatible)
The full text of the license can be found in the LICENSE file included
with this distribution.
perl v5.34.0 2022-06-21 Specio::Coercion(3pm)
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