class::struct.3

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.\" ========================================================================
.\"
.IX Title "Class::Struct 3"
.TH Class::Struct 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
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.SH "NAME"
Class::Struct \- declare struct\-like datatypes as Perl classes
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 5
\&    use Class::Struct;
\&            # declare struct, based on array:
\&    struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ]);
\&            # declare struct, based on hash:
\&    struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });
\&
\&    package CLASS_NAME;
\&    use Class::Struct;
\&            # declare struct, based on array, implicit class name:
\&    struct( ELEMENT_NAME => ELEMENT_TYPE, ... );
\&
\&    # Declare struct at compile time
\&    use Class::Struct CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ];
\&    use Class::Struct CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... };
\&
\&    # declare struct at compile time, based on array, implicit class name:
\&    package CLASS_NAME;
\&    use Class::Struct ELEMENT_NAME => ELEMENT_TYPE, ... ;
\&
\&    package Myobj;
\&    use Class::Struct;
\&            # declare struct with four types of elements:
\&    struct( s => \*(Aq$\*(Aq, a => \*(Aq@\*(Aq, h => \*(Aq%\*(Aq, c => \*(AqMy_Other_Class\*(Aq );
\&
\&    $obj = new Myobj;               # constructor
\&
\&                                    # scalar type accessor:
\&    $element_value = $obj\->s;           # element value
\&    $obj\->s(\*(Aqnew value\*(Aq);               # assign to element
\&
\&                                    # array type accessor:
\&    $ary_ref = $obj\->a;                 # reference to whole array
\&    $ary_element_value = $obj\->a(2);    # array element value
\&    $obj\->a(2, \*(Aqnew value\*(Aq);            # assign to array element
\&
\&                                    # hash type accessor:
\&    $hash_ref = $obj\->h;                # reference to whole hash
\&    $hash_element_value = $obj\->h(\*(Aqx\*(Aq); # hash element value
\&    $obj\->h(\*(Aqx\*(Aq, \*(Aqnew value\*(Aq);          # assign to hash element
\&
\&                                    # class type accessor:
\&    $element_value = $obj\->c;           # object reference
\&    $obj\->c\->method(...);               # call method of object
\&    $obj\->c(new My_Other_Class);        # assign a new object
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`Class::Struct\*(C'\fR exports a single function, \f(CW\*(C`struct\*(C'\fR.
Given a list of element names and types, and optionally
a class name, \f(CW\*(C`struct\*(C'\fR creates a Perl 5 class that implements
a \*(L"struct-like\*(R" data structure.
.PP
The new class is given a constructor method, \f(CW\*(C`new\*(C'\fR, for creating
struct objects.
.PP
Each element in the struct data has an accessor method, which is
used to assign to the element and to fetch its value.  The
default accessor can be overridden by declaring a \f(CW\*(C`sub\*(C'\fR of the
same name in the package.  (See Example 2.)
.PP
Each element's type can be scalar, array, hash, or class.
.ie n .Sh "The ""struct()"" function"
.el .Sh "The \f(CWstruct()\fP function"
.IX Subsection "The struct() function"
The \f(CW\*(C`struct\*(C'\fR function has three forms of parameter-list.
.PP
.Vb 3
\&    struct( CLASS_NAME => [ ELEMENT_LIST ]);
\&    struct( CLASS_NAME => { ELEMENT_LIST });
\&    struct( ELEMENT_LIST );
.Ve
.PP
The first and second forms explicitly identify the name of the
class being created.  The third form assumes the current package
name as the class name.
.PP
An object of a class created by the first and third forms is
based on an array, whereas an object of a class created by the
second form is based on a hash. The array-based forms will be
somewhat faster and smaller; the hash-based forms are more
flexible.
.PP
The class created by \f(CW\*(C`struct\*(C'\fR must not be a subclass of another
class other than \f(CW\*(C`UNIVERSAL\*(C'\fR.
.PP
It can, however, be used as a superclass for other classes. To facilitate
this, the generated constructor method uses a two-argument blessing.
Furthermore, if the class is hash-based, the key of each element is
prefixed with the class name (see \fIPerl Cookbook\fR, Recipe 13.12).
.PP
A function named \f(CW\*(C`new\*(C'\fR must not be explicitly defined in a class
created by \f(CW\*(C`struct\*(C'\fR.
.PP
The \fI\s-1ELEMENT_LIST\s0\fR has the form
.PP
.Vb 1
\&    NAME => TYPE, ...
.Ve
.PP
Each name-type pair declares one element of the struct. Each
element name will be defined as an accessor method unless a
method by that name is explicitly defined; in the latter case, a
warning is issued if the warning flag (\fB\-w\fR) is set.
.Sh "Class Creation at Compile Time"
.IX Subsection "Class Creation at Compile Time"
\&\f(CW\*(C`Class::Struct\*(C'\fR can create your class at compile time.  The main reason
for doing this is obvious, so your class acts like every other class in
Perl.  Creating your class at compile time will make the order of events
similar to using any other class ( or Perl module ).
.PP
There is no significant speed gain between compile time and run time
class creation, there is just a new, more standard order of events.
.Sh "Element Types and Accessor Methods"
.IX Subsection "Element Types and Accessor Methods"
The four element types \*(-- scalar, array, hash, and class \*(-- are
represented by strings \*(-- \f(CW\*(Aq$\*(Aq\fR, \f(CW\*(Aq@\*(Aq\fR, \f(CW\*(Aq%\*(Aq\fR, and a class name \*(--
optionally preceded by a \f(CW\*(Aq*\*(Aq\fR.
.PP
The accessor method provided by \f(CW\*(C`struct\*(C'\fR for an element depends
on the declared type of the element.
.ie n .IP "Scalar (\*(Aq$\*(Aq\fR or \f(CW\*(Aq*$\*(Aq)" 4
.el .IP "Scalar (\f(CW\*(Aq$\*(Aq\fR or \f(CW\*(Aq*$\*(Aq\fR)" 4