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.\" ========================================================================
.\"
.IX Title "Scalar::Does 3pm"
.TH Scalar::Does 3pm 2024-01-21 "perl v5.38.2" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
Scalar::Does \- like ref() but useful
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\&  use Scalar::Does qw( \-constants );
\&  
\&  my $object = bless {}, \*(AqSome::Class\*(Aq;
\&  
\&  does($object, \*(AqSome::Class\*(Aq);   # true
\&  does($object, \*(Aq%{}\*(Aq);           # true
\&  does($object, HASH);            # true
\&  does($object, ARRAY);           # false
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
It has long been noted that Perl would benefit from a \f(CWdoes()\fR built-in.
A check that \f(CW\*(C`ref($thing) eq \*(AqARRAY\*(Aq\*(C'\fR doesn't allow you to accept an
object that uses overloading to provide an array-like interface.
.SS Functions
.IX Subsection "Functions"
.ie n .IP """does($scalar, $role)""" 4
.el .IP "\f(CWdoes($scalar, $role)\fR" 4
.IX Item "does($scalar, $role)"
Checks if a scalar is capable of performing the given role. The following
(case-sensitive) roles are predefined:
.RS 4
.IP \(bu 4
\&\fBSCALAR\fR or \fB${}\fR
.Sp
Checks if the scalar can be used as a scalar reference.
.Sp
Note: this role does not check whether a scalar is a scalar (which is
obviously true) but whether it is a reference to another scalar.
.IP \(bu 4
\&\fBARRAY\fR or \fB@{}\fR
.Sp
Checks if the scalar can be used as an array reference.
.IP \(bu 4
\&\fBHASH\fR or \fB%{}\fR
.Sp
Checks if the scalar can be used as a hash reference.
.IP \(bu 4
\&\fBCODE\fR or \fB&{}\fR
.Sp
Checks if the scalar can be used as a code reference.
.IP \(bu 4
\&\fBGLOB\fR or \fB*{}\fR
.Sp
Checks if the scalar can be used as a glob reference.
.IP \(bu 4
\&\fBREF\fR
.Sp
Checks if the scalar can be used as a ref reference (i.e. a reference to
another reference).
.IP \(bu 4
\&\fBLVALUE\fR
.Sp
Checks if the scalar is a reference to a special lvalue (e.g. the result
of \f(CW\*(C`substr\*(C'\fR or \f(CW\*(C`splice\*(C'\fR).
.IP \(bu 4
\&\fBIO\fR or \fB<>\fR
.Sp
Uses IO::Detect to check if the scalar is a filehandle or file-handle-like
object.
.Sp
(The \f(CW\*(C`<>\*(C'\fR check is slightly looser, allowing objects which overload
\&\f(CW\*(C`<>\*(C'\fR, though overloading \f(CW\*(C`<>\*(C'\fR well can be a little tricky.)
.IP \(bu 4
\&\fBVSTRING\fR
.Sp
Checks if the scalar is a vstring reference.
.IP \(bu 4
\&\fBFORMAT\fR
.Sp
Checks if the scalar is a format reference.
.IP \(bu 4
\&\fBRegexp\fR or \fBqr\fR
.Sp
Checks if the scalar can be used as a quoted regular expression.
.IP \(bu 4
\&\fBbool\fR
.Sp
Checks if the scalar can be used as a boolean. (It's pretty rare for this
to not be true.)
.IP \(bu 4
\&\fB""\fR
.Sp
Checks if the scalar can be used as a string. (It's pretty rare for this
to not be true.)
.IP \(bu 4
\&\fB0+\fR
.Sp
Checks if the scalar can be used as a number. (It's pretty rare for this
to not be true.)
.Sp
Note that this is far looser than \f(CW\*(C`looks_like_number\*(C'\fR from Scalar::Util.
For example, an unblessed arrayref can be used as a number (it numifies to
its reference address); the string "Hello World" can be used as a number (it
numifies to 0).
.IP \(bu 4
\&\fB~~\fR
.Sp
Checks if the scalar can be used on the right hand side of a smart match.
.RE
.RS 4
.Sp
If the given \fIrole\fR is blessed, and provides a \f(CW\*(C`check\*(C'\fR method, then
\&\f(CW\*(C`does\*(C'\fR delegates to that.
.Sp
Otherwise, if the scalar being tested is blessed, then
\&\f(CW\*(C`$scalar\->DOES($role)\*(C'\fR is called, and \f(CW\*(C`does\*(C'\fR returns true if
the method call returned true.
.Sp
If the scalar being tested looks like a Perl class name, then 
\&\f(CW\*(C`$scalar\->DOES($role)\*(C'\fR is also called, and the string "0E0" is
returned for success, which evaluates to 0 in a numeric context but
true in a boolean context.
.RE
.ie n .IP does($role) 4
.el .IP \f(CWdoes($role)\fR 4
.IX Item "does($role)"
Called with a single argument, tests \f(CW$_\fR. Yes, this works with lexical
\&\f(CW$_\fR.
.Sp
.Vb 4
\&  given ($object) {
\&     when(does ARRAY)  { ... }
\&     when(does HASH)   { ... }
\&  }
.Ve
.Sp
Note: in Scalar::Does 0.007 and below the single-argument form of \f(CW\*(C`does\*(C'\fR
returned a curried coderef. This was changed in Scalar::Does 0.008.
.ie n .IP """overloads($scalar, $role)""" 4
.el .IP "\f(CWoverloads($scalar, $role)\fR" 4
.IX Item "overloads($scalar, $role)"
A function \f(CW\*(C`overloads\*(C'\fR (which just checks overloading) is also available.
.ie n .IP overloads($role) 4
.el .IP \f(CWoverloads($role)\fR 4
.IX Item "overloads($role)"
Called with a single argument, tests \f(CW$_\fR. Yes, this works with lexical
\&\f(CW$_\fR.
.Sp
Note: in Scalar::Does 0.007 and below the single-argument form of \f(CW\*(C`overloads\*(C'\fR
returned a curried coderef. This was changed in Scalar::Does 0.008.
.ie n .IP "blessed($scalar), reftype($scalar), looks_like_number($scalar)" 4
.el .IP "\f(CWblessed($scalar)\fR, \f(CWreftype($scalar)\fR, \f(CWlooks_like_number($scalar)\fR" 4
.IX Item "blessed($scalar), reftype($scalar), looks_like_number($scalar)"
For convenience, this module can also re-export these functions from
Scalar::Util. \f(CW\*(C`looks_like_number\*(C'\fR is generally more useful than
\&\f(CW\*(C`does($scalar, q[0+])\*(C'\fR.
.ie n .IP """make_role $name, where { BLOCK }""" 4
.el .IP "\f(CWmake_role $name, where { BLOCK }\fR" 4
.IX Item "make_role $name, where { BLOCK }"
Returns an anonymous role object which can be used as a parameter to
\&\f(CW\*(C`does\*(C'\fR. The block is arbitrary code which should check whether \f(CW$_\fR[0]
does the role.
.ie n .IP """where { BLOCK }""" 4
.el .IP "\f(CWwhere { BLOCK }\fR" 4
.IX Item "where { BLOCK }"
Syntactic sugar for \f(CW\*(C`make_role\*(C'\fR. Compatible with the \f(CW\*(C`where\*(C'\fR function
from Moose::Util::TypeConstraints, so don't worry about conflicts.
.SS Constants
.IX Subsection "Constants"
The following constants may be exported for convenience:
.ie n .IP """SCALAR""" 4
.el .IP \f(CWSCALAR\fR 4
.IX Item "SCALAR"
.PD 0
.ie n .IP """ARRAY""" 4
.el .IP \f(CWARRAY\fR 4
.IX Item "ARRAY"
.ie n .IP """HASH""" 4
.el .IP \f(CWHASH\fR 4
.IX Item "HASH"
.ie n .IP """CODE""" 4
.el .IP \f(CWCODE\fR 4
.IX Item "CODE"
.ie n .IP """GLOB""" 4
.el .IP \f(CWGLOB\fR 4
.IX Item "GLOB"
.ie n .IP """REF""" 4
.el .IP \f(CWREF\fR 4
.IX Item "REF"
.ie n .IP """LVALUE""" 4
.el .IP \f(CWLVALUE\fR 4
.IX Item "LVALUE"
.ie n .IP """IO""" 4
.el .IP \f(CWIO\fR 4
.IX Item "IO"
.ie n .IP """VSTRING""" 4
.el .IP \f(CWVSTRING\fR 4
.IX Item "VSTRING"
.ie n .IP """FORMAT""" 4
.el .IP \f(CWFORMAT\fR 4
.IX Item "FORMAT"
.ie n .IP """REGEXP""" 4
.el .IP \f(CWREGEXP\fR 4
.IX Item "REGEXP"
.ie n .IP """BOOLEAN""" 4
.el .IP \f(CWBOOLEAN\fR 4
.IX Item "BOOLEAN"
.ie n .IP """STRING""" 4
.el .IP \f(CWSTRING\fR 4
.IX Item "STRING"
.ie n .IP """NUMBER""" 4
.el .IP \f(CWNUMBER\fR 4
.IX Item "NUMBER"
.ie n .IP """SMARTMATCH""" 4
.el .IP \f(CWSMARTMATCH\fR 4
.IX Item "SMARTMATCH"
.PD
.SS Export
.IX Subsection "Export"
By default, only \f(CW\*(C`does\*(C'\fR is exported. This module uses Exporter::Tiny, so
functions can be renamed:
.PP
.Vb 1
\&  use Scalar::Does does => { \-as => \*(Aqperforms_role\*(Aq };
.Ve
.PP
Scalar::Does also plays some tricks with namespace::clean to ensure that
any functions it exports to your namespace are cleaned up when you're finished
with them. This ensures that if you're writing object-oriented code \f(CW\*(C`does\*(C'\fR
and \f(CW\*(C`overloads\*(C'\fR will not be left hanging around as methods of your classes.
Moose::Object provides a \f(CW\*(C`does\*(C'\fR method, and you should be able to use
Scalar::Does without interfering with that.
.PP
You can import the constants (plus \f(CW\*(C`does\*(C'\fR) using:
.PP
.Vb 1
\&  use Scalar::Does \-constants;
.Ve
.PP
The \f(CW\*(C`make_role\*(C'\fR and \f(CW\*(C`where\*(C'\fR functions can be exported like this:
.PP
.Vb 1
\&  use Scalar::Does \-make;
.Ve
.PP
Or list specific functions/constants that you wish to import:
.PP
.Vb 1
\&  use Scalar::Does qw( does ARRAY HASH STRING NUMBER );
.Ve
.SS "Custom Role Checks"
.IX Subsection "Custom Role Checks"
.Vb 3
\&  use Scalar::Does
\&    custom => { \-as => \*(Aqdoes_array\*(Aq, \-role => \*(AqARRAY\*(Aq },
\&    custom => { \-as => \*(Aqdoes_hash\*(Aq,  \-role => \*(AqHASH\*(Aq  };
\&  
\&  does_array($thing);
\&  does_hash($thing);
.Ve
.SH BUGS
.IX Header "BUGS"
Please report any bugs to
<http://rt.cpan.org/Dist/Display.html?Queue=Scalar\-Does>.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Scalar::Util.
.PP
<http://perldoc.perl.org/5.10.0/perltodo.html#A\-\fBdoes()\fR\-built\-in>.
.SS "Relationship to Moose roles"
.IX Subsection "Relationship to Moose roles"
Scalar::Does is not dependent on Moose, and its role-checking is not specific
to Moose's idea of roles, but it does work well with Moose roles.
.PP
Moose::Object overrides \f(CW\*(C`DOES\*(C'\fR, so Moose objects and Moose roles should
"just work" with Scalar::Does.
.PP
.Vb 4
\&  {
\&    package Transport;
\&    use Moose::Role;
\&  }
\&  
\&  {
\&    package Train;
\&    use Moose;
\&    with qw(Transport);
\&  }
\&  
\&  my $thomas = Train\->new;
\&  does($thomas, \*(AqTrain\*(Aq);          # true
\&  does($thomas, \*(AqTransport\*(Aq);      # true
\&  does($thomas, Transport\->meta);  # not yet supported!
.Ve
.PP
Mouse::Object should be compatible enough to work as well.
.PP
See also:
Moose::Role,
Moose::Object,
UNIVERSAL.
.SS "Relationship to Moose type constraints"
.IX Subsection "Relationship to Moose type constraints"
Moose::Meta::TypeConstraint objects, plus the constants exported by
MooseX::Types libraries all provide a \f(CW\*(C`check\*(C'\fR method, so again, should
"just work" with Scalar::Does. Type constraint strings are not supported
however.
.PP
.Vb 3
\&  use Moose::Util::TypeConstraints qw(find_type_constraint);
\&  use MooseX::Types qw(Int);
\&  use Scalar::Does qw(does);
\&  
\&  my $int = find_type_constraint("Int");
\&  
\&  does( "123", $int );     # true
\&  does( "123", Int );      # true
\&  does( "123", "Int" );    # false
.Ve
.PP
Mouse::Meta::TypeConstraints and MouseX::Types should be compatible
enough to work as well.
.PP
See also:
Moose::Meta::TypeConstraint,
Moose::Util::TypeConstraints,
MooseX::Types,
Scalar::Does::MooseTypes.
.SS "Relationship to Type::Tiny type constraints"
.IX Subsection "Relationship to Type::Tiny type constraints"
Types built with Type::Tiny and Type::Library can be used exactly as
Moose type constraint objects above.
.PP
.Vb 2
\&  use Types::Standard qw(Int);
\&  use Scalar::Does qw(does);
\&  
\&  does(123, Int);   # true
.Ve
.PP
In fact, Type::Tiny and related libraries are used extensively in the
internals of Scalar::Does 0.200+.
.PP
See also:
Type::Tiny,
Types::Standard.
.SS "Relationship to Role::Tiny and Moo roles"
.IX Subsection "Relationship to Role::Tiny and Moo roles"
Roles using Role::Tiny 1.002000 and above provide a \f(CW\*(C`DOES\*(C'\fR method, so
should work with Scalar::Does just like Moose roles. Prior to that release,
Role::Tiny did not provide \f(CW\*(C`DOES\*(C'\fR.
.PP
Moo's role system is based on Role::Tiny.
.PP
See also:
Role::Tiny,
Moo::Role.
.SH AUTHOR
.IX Header "AUTHOR"
Toby Inkster <tobyink@cpan.org>.
.SH "COPYRIGHT AND LICENCE"
.IX Header "COPYRIGHT AND LICENCE"
This software is copyright (c) 2012\-2014, 2017 by Toby Inkster.
.PP
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
.SH "DISCLAIMER OF WARRANTIES"
.IX Header "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.