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1 | =pod |
2 | |
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3 | =head1 NAME |
4 | |
5 | Moose::Manual::BestPractices - Get the most out of Moose |
6 | |
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7 | =head1 RECOMMENDATIONS |
8 | |
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9 | Moose has a lot of features, and there's definitely more than one way |
10 | to do it. However, we think that picking a subset of these features |
11 | and using them consistently makes everyone's life easier. |
12 | |
13 | Of course, as with any list of "best practices", these are really just |
14 | opinions. Feel free to ignore us. |
15 | |
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16 | =head2 C<no Moose> and immutabilize |
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17 | |
18 | We recommend that you end your Moose class definitions by removing the |
19 | Moose sugar and making your class immutable. |
20 | |
21 | package Person; |
22 | |
23 | use Moose; |
24 | |
25 | # extends, roles, attributes, etc. |
26 | |
27 | # methods |
28 | |
29 | no Moose; |
30 | |
31 | __PACKAGE__->meta->make_immutable; |
32 | |
33 | 1; |
34 | |
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35 | The C<no Moose> bit is simply good code hygiene, as it removes all the |
36 | Moose keywords from your class's namespace. Once the class has been |
37 | built, these keywords are not needed needed. The C<make_immutable> |
38 | call allows Moose to speed up a lot of things, most notably object |
39 | construction. The tradeoff is that you can no longer change the class |
40 | definition. |
41 | |
42 | A more generic way to unimport not only L<Moose>'s exports but also |
43 | those from type libraries and other modules is to use |
44 | L<namespace::clean> or L<namespace::autoclean>. |
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45 | |
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46 | =head2 Never override C<new> |
47 | |
48 | Overriding C<new> is a very bad practice. Instead, you should use a |
49 | C<BUILD> or C<BUILDARGS> methods to do the same thing. When you |
50 | override C<new>, Moose can no longer inline a constructor when your |
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51 | class is immutabilized. |
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52 | |
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53 | There are two good reasons to override C<new>. One, you are writing a |
54 | MooseX extension that provides its own L<Moose::Object> subclass |
55 | I<and> a subclass of L<Moose::Meta::Method::Constructor> to inline the |
56 | constructor. Two, you are subclassing a non-Moose parent. |
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57 | |
58 | If you know how to do that, you know when to ignore this best practice |
59 | ;) |
60 | |
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61 | =head2 Always call C<SUPER::BUILDARGS> |
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62 | |
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63 | If you override the C<BUILDARGS> method in your class, make sure to |
64 | play nice and call C<SUPER::BUILDARGS> to handle cases you're not |
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65 | checking for explicitly. |
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66 | |
67 | The default C<BUILDARGS> method in L<Moose::Object> handles both a |
68 | list and hashref of named parameters correctly, and also checks for a |
69 | I<non-hashref> single argument. |
70 | |
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71 | =head2 Provide defaults whenever possible, otherwise use C<required> |
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72 | |
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73 | When your class provides defaults, this makes constructing new objects |
74 | simpler. If you cannot provide a default, consider making the |
75 | attribute C<required>. |
76 | |
77 | If you don't do either, an attribute can simply be left unset, |
78 | increasing the complexity of your object, because it has more possible |
79 | states that you or the user of your class must account for. |
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80 | |
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81 | =head2 Use C<builder> instead of C<default> most of the time |
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82 | |
83 | Builders can be inherited, they have explicit names, and they're just |
84 | plain cleaner. |
85 | |
86 | However, I<do> use a default when the default is a non-reference, |
87 | I<or> when the default is simply an empty reference of some sort. |
88 | |
89 | Also, keep your builder methods private. |
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90 | |
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91 | =head2 Use C<lazy_build> |
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92 | |
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93 | Lazy is good, and often solves initialization ordering problems. It's |
94 | also good for deferring work that may never have to be done. If you're |
95 | going to be lazy, use I<lazy_build> to save yourself some typing and |
96 | standardize names. |
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97 | |
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98 | =head2 Consider keeping clearers and predicates private |
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99 | |
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100 | Does everyone I<really> need to be able to clear an attribute? |
101 | Probably not. Don't expose this functionality outside your class |
102 | by default. |
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103 | |
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104 | Predicates are less problematic, but there's no reason to make your |
105 | public API bigger than it has to be. |
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106 | |
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107 | =head2 Default to read-only, and consider keeping writers private |
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108 | |
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109 | Making attributes mutable just means more complexity to account for in |
110 | your program. The alternative to mutable state is to encourage users |
111 | of your class to simply make new objects as needed. |
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112 | |
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113 | If you I<must> make an attribute read-write, consider making the |
114 | writer a separate private method. Narrower APIs are easy to maintain, |
115 | and mutable state is trouble. |
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116 | |
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117 | In order to declare such attributes, provide a private C<writer> |
118 | parameter: |
119 | |
120 | has pizza => ( |
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121 | is => 'ro', |
122 | isa => 'Pizza', |
123 | writer => '_pizza', |
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124 | ); |
125 | |
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126 | =head2 Think twice before changing an attribute's type in a subclass |
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127 | |
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128 | Down this path lies great confusion. If the attribute is an object |
129 | itself, at least make sure that it has the same interface as the type |
130 | of object in the parent class. |
131 | |
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132 | =head2 Don't use the C<initializer> feature |
133 | |
134 | Don't know what we're talking about? That's fine. |
135 | |
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136 | =head2 Use L<MooseX::AttributeHelpers> instead of C<auto_deref> |
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137 | |
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138 | The C<auto_deref> feature is a bit troublesome. Directly exposing a |
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139 | complex attribute is ugly. Instead, consider using |
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140 | L<MooseX::AttributeHelpers> to define an API that exposes those pieces |
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141 | of functionality that need exposing. Then you can expose just the |
142 | functionality that you want. |
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143 | |
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144 | =head2 Always call C<inner> in the most specific subclass |
145 | |
146 | When using C<augment> and C<inner>, we recommend that you call |
147 | C<inner> in the most specific subclass of your hierarchy. This makes |
148 | it possible to subclass further and extend the hierarchy without |
149 | changing the parents. |
150 | |
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151 | =head2 Namespace your types |
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152 | |
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153 | Use some sort of namespacing convention for type names. We recommend |
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154 | something like "MyApp::Type::Foo". |
155 | |
156 | If you're intending to package your types up for re-use using |
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157 | L<MooseX::Types> later, avoid using characters that are invalid in |
158 | perl identifiers such as a space or period. |
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159 | |
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160 | =head2 Do not coerce Moose built-ins directly |
161 | |
162 | If you define a coercion for a Moose built-in like C<ArrayRef>, this |
163 | will affect every application in the Perl interpreter that uses this |
164 | type. |
165 | |
166 | # very naughty! |
167 | coerce 'ArrayRef' |
168 | => from Str |
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169 | => via { [ split /,/ ] }; |
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170 | |
171 | Instead, create a subtype and coerce that: |
172 | |
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173 | subtype 'My::ArrayRef' => as 'ArrayRef'; |
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174 | |
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175 | coerce 'My::ArrayRef' |
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176 | => from 'Str' |
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177 | => via { [ split /,/ ] }; |
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178 | |
179 | =head2 Do not coerce class names directly |
180 | |
181 | Just as with Moose built-in types, a class type is global for the |
182 | entire interpreter. If you add a coercion for that class name, it can |
183 | have magical side effects elsewhere: |
184 | |
185 | # also very naughty! |
186 | coerce 'HTTP::Headers' |
187 | => from 'HashRef' |
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188 | => via { HTTP::Headers->new( %{$_} ) }; |
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189 | |
190 | Instead, we can create an "empty" subtype for the coercion: |
191 | |
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192 | subtype 'My::HTTP::Headers' => as class_type('HTTP::Headers'); |
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193 | |
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194 | coerce 'My::HTTP::Headers' |
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195 | => from 'HashRef' |
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196 | => via { HTTP::Headers->new( %{$_} ) }; |
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197 | |
198 | =head2 Use coercion instead of unions |
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199 | |
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200 | Consider using a type coercion instead of a type union. This was |
201 | covered at length in L<Moose::Manual::Types>. |
202 | |
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203 | =head2 Define all your types in one module |
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204 | |
205 | Define all your types and coercions in one module. This was also |
206 | covered in L<Moose::Manual::Types>. |
207 | |
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208 | =head1 BENEFITS OF BEST PRACTICES |
209 | |
210 | Following these practices has a number of benefits. |
211 | |
212 | It helps ensure that your code will play nice with others, making it |
213 | more reusable and easier to extend. |
214 | |
215 | Following an accepted set of idioms will make maintenance easier, |
216 | especially when someone else has to maintain your code. It will also |
217 | make it easier to get support from other Moose users, since your code |
218 | will be easier to digest quickly. |
219 | |
220 | Some of these practices are designed to help Moose do the right thing, |
221 | especially when it comes to immutabilization. This means your code |
222 | will be faster when immutabilized. |
223 | |
224 | Many of these practices also help get the most out of meta |
225 | programming. If you used an overridden C<new> to do type coercion by |
226 | hand, rather than defining a real coercion, there is no introspectable |
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227 | metadata. This sort of thing is particularly problematic for MooseX |
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228 | extensions which rely on introspection to do the right thing. |
229 | |
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230 | =head1 AUTHOR |
231 | |
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232 | Yuval (nothingmuch) Kogman |
233 | |
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234 | Dave Rolsky E<lt>autarch@urth.orgE<gt> |
235 | |
236 | =head1 COPYRIGHT AND LICENSE |
237 | |
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238 | Copyright 2009 by Infinity Interactive, Inc. |
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239 | |
240 | L<http://www.iinteractive.com> |
241 | |
242 | This library is free software; you can redistribute it and/or modify |
243 | it under the same terms as Perl itself. |
244 | |
245 | =cut |