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.IX Title "Object::Pad::ClassAttr::Struct 3pm"
.TH Object::Pad::ClassAttr::Struct 3pm 2024-03-07 "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.
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.SH NAME
"Object::Pad::ClassAttr::Struct" \- declare an "Object::Pad" class to be struct\-like
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\&   use Object::Pad;
\&   use Object::Pad::ClassAttr::Struct;
\&
\&   class Colour :Struct {
\&      # These get :param :mutator automatically
\&      field $red   = 0;
\&      field $green = 0;
\&      field $blue  = 0;
\&
\&      # Additional methods are still permitted
\&      method lightness {
\&         return ($red + $green + $blue) / 3;
\&      }
\&   }
\&
\&   my $cyan = Colour\->new( green => 1, blue => 1 );
\&
\&   # A positional constructor is created automatically
\&   my $white = Colour\->new_values(1, 1, 1);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
This module provides a third-party class attribute for Object::Pad\-based
classes, which applies some attributes automatically to every field added to
the class, as a convenient shortcut for making structure-like classes.
.SH "CLASS ATTRIBUTES"
.IX Header "CLASS ATTRIBUTES"
.SS :Struct
.IX Subsection ":Struct"
.Vb 1
\&   class Name :Struct ... { ... }
.Ve
.PP
Automatically applies the \f(CW\*(C`:param\*(C'\fR and \f(CW\*(C`:mutator\*(C'\fR attributes to every field
defined on the class, meaning the constructor will accept parameters for each
field to initialise the value, and each field will have an lvalue mutator
method.
.PP
In addition, the class itself gains the \f(CW:strict(params)\fR attribute, meaning
the constructor will check parameter names and throw an exception for
unrecognised names.
.PP
\&\fISince version 0.04\fR a positional constructor class method called
\&\f(CW\*(C`new_values\*(C'\fR is also provided into the class, which takes a value for every
field positionally, in declared order.
.PP
.Vb 1
\&   $obj = ClassName\->new_values($v1, $v2, $v3, ...);
.Ve
.PP
This positional constructor must receive as many positional arguments as there
are fields in total in the class; even the optional ones. All arguments are
required here.
.PP
\&\fISince version 0.05\fR the following options are permitted inside the attribute
value parentheses:
.PP
\fI:Struct(readonly)\fR
.IX Subsection ":Struct(readonly)"
.PP
Instances of this class do not permit fields to be modified after
construction. The accessor is created using the \f(CW\*(C`:reader\*(C'\fR field attribute
rather than \f(CW\*(C`:mutator\*(C'\fR.
.SH AUTHOR
.IX Header "AUTHOR"
Paul Evans <leonerd@leonerd.org.uk>