.\" Automatically generated by Pod::Man 4.10 (Pod::Simple 3.35) .\" .\" Standard preamble: .\" ======================================================================== .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left .\" double quote, and \*(R" will give a right double quote. \*(C+ will .\" give a nicer C++. Capital omega is used to do unbreakable dashes and .\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff, .\" nothing in troff, for use with C<>. .tr \(*W- .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' .ie n \{\ . ds -- \(*W- . ds PI pi . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch . ds L" "" . ds R" "" . ds C` "" . ds C' "" 'br\} .el\{\ . ds -- \|\(em\| . ds PI \(*p . ds L" `` . ds R" '' . ds C` . ds C' 'br\} .\" .\" Escape single quotes in literal strings from groff's Unicode transform. .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" .\" If the F register is >0, we'll generate index entries on stderr for .\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index .\" entries marked with X<> in POD. Of course, you'll have to process the .\" output yourself in some meaningful fashion. .\" .\" Avoid warning from groff about undefined register 'F'. .de IX .. .nr rF 0 .if \n(.g .if rF .nr rF 1 .if (\n(rF:(\n(.g==0)) \{\ . if \nF \{\ . de IX . tm Index:\\$1\t\\n%\t"\\$2" .. . if !\nF==2 \{\ . nr % 0 . nr F 2 . \} . \} .\} .rr rF .\" ======================================================================== .\" .IX Title "Moose::Cookbook::Basics::Person_BUILDARGSAndBUILD 3pm" .TH Moose::Cookbook::Basics::Person_BUILDARGSAndBUILD 3pm "2018-11-02" "perl v5.28.0" "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" Moose::Cookbook::Basics::Person_BUILDARGSAndBUILD \- Using BUILDARGS and BUILD to hook into object construction .SH "VERSION" .IX Header "VERSION" version 2.2011 .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& package Person; \& \& has \*(Aqssn\*(Aq => ( \& is => \*(Aqro\*(Aq, \& isa => \*(AqStr\*(Aq, \& predicate => \*(Aqhas_ssn\*(Aq, \& ); \& \& has \*(Aqcountry_of_residence\*(Aq => ( \& is => \*(Aqro\*(Aq, \& isa => \*(AqStr\*(Aq, \& default => \*(Aqusa\*(Aq \& ); \& \& has \*(Aqfirst_name\*(Aq => ( \& is => \*(Aqro\*(Aq, \& isa => \*(AqStr\*(Aq, \& ); \& \& has \*(Aqlast_name\*(Aq => ( \& is => \*(Aqro\*(Aq, \& isa => \*(AqStr\*(Aq, \& ); \& \& around BUILDARGS => sub { \& my $orig = shift; \& my $class = shift; \& \& if ( @_ == 1 && ! ref $_[0] ) { \& return $class\->$orig(ssn => $_[0]); \& } \& else { \& return $class\->$orig(@_); \& } \& }; \& \& sub BUILD { \& my $self = shift; \& \& if ( $self\->country_of_residence eq \*(Aqusa\*(Aq ) { \& die \*(AqCannot create a Person who lives in the USA without an ssn.\*(Aq \& unless $self\->has_ssn; \& } \& } .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" This recipe demonstrates the use of \f(CW\*(C`BUILDARGS\*(C'\fR and \f(CW\*(C`BUILD\*(C'\fR. By defining these methods, we can hook into the object construction process without overriding \f(CW\*(C`new\*(C'\fR. .PP The \f(CW\*(C`BUILDARGS\*(C'\fR method is called \fIbefore\fR an object has been created. It is called as a class method, and receives all of the parameters passed to the \f(CW\*(C`new\*(C'\fR method. It is expected to do something with these arguments and return a hash reference. The keys of the hash must be attribute \f(CW\*(C`init_arg\*(C'\fRs. .PP The primary purpose of \f(CW\*(C`BUILDARGS\*(C'\fR is to allow a class to accept something other than named arguments. In the case of our \f(CW\*(C`Person\*(C'\fR class, we are allowing it to be called with a single argument, a social security number: .PP .Vb 1 \& my $person = Person\->new(\*(Aq123\-45\-6789\*(Aq); .Ve .PP The key part of our \f(CW\*(C`BUILDARGS\*(C'\fR is this conditional: .PP .Vb 3 \& if ( @_ == 1 && ! ref $_[0] ) { \& return $class\->$orig(ssn => $_[0]); \& } .Ve .PP By default, Moose constructors accept a list of key-value pairs, or a hash reference. We need to make sure that \f(CW$_[0]\fR is not a reference before assuming it is a social security number. .PP We call the original \f(CW\*(C`BUILDARGS\*(C'\fR method to handle all the other cases. You should always do this in your own \f(CW\*(C`BUILDARGS\*(C'\fR methods, since Moose::Object provides its own \f(CW\*(C`BUILDARGS\*(C'\fR method that handles hash references and a list of key-value pairs. .PP The \f(CW\*(C`BUILD\*(C'\fR method is called \fIafter\fR the object is constructed, but before it is returned to the caller. The \f(CW\*(C`BUILD\*(C'\fR method provides an opportunity to check the object state as a whole. This is a good place to put logic that cannot be expressed as a type constraint on a single attribute. .PP In the \f(CW\*(C`Person\*(C'\fR class, we need to check the relationship between two attributes, \f(CW\*(C`ssn\*(C'\fR and \f(CW\*(C`country_of_residence\*(C'\fR. We throw an exception if the object is not logically consistent. .SH "MORE CONSIDERATIONS" .IX Header "MORE CONSIDERATIONS" This recipe is made significantly simpler because all of the attributes are read-only. If the \f(CW\*(C`country_of_residence\*(C'\fR attribute were settable, we would need to check that a Person had an \f(CW\*(C`ssn\*(C'\fR if the new country was \f(CW\*(C`usa\*(C'\fR. This could be done with a \f(CW\*(C`before\*(C'\fR modifier. .SH "CONCLUSION" .IX Header "CONCLUSION" We have repeatedly discouraged overriding \f(CW\*(C`new\*(C'\fR in Moose classes. This recipe shows how you can use \f(CW\*(C`BUILDARGS\*(C'\fR and \f(CW\*(C`BUILD\*(C'\fR to hook into object construction without overriding \f(CW\*(C`new\*(C'\fR. .PP The \f(CW\*(C`BUILDARGS\*(C'\fR method lets us expand on Moose's built-in parameter handling for constructors. The \f(CW\*(C`BUILD\*(C'\fR method lets us implement logical constraints across the whole object after it is created. .SH "AUTHORS" .IX Header "AUTHORS" .IP "\(bu" 4 Stevan Little .IP "\(bu" 4 Dave Rolsky .IP "\(bu" 4 Jesse Luehrs .IP "\(bu" 4 Shawn M Moore .IP "\(bu" 4 יובל קוג'מן (Yuval Kogman) .IP "\(bu" 4 Karen Etheridge .IP "\(bu" 4 Florian Ragwitz .IP "\(bu" 4 Hans Dieter Pearcey .IP "\(bu" 4 Chris Prather .IP "\(bu" 4 Matt S Trout .SH "COPYRIGHT AND LICENSE" .IX Header "COPYRIGHT AND LICENSE" This software is copyright (c) 2006 by Infinity Interactive, Inc. .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.