Takes some boilerplate out of Ruby, lowering the barrier to extracting small focused classes, without the downsides of using Struct.
Instead of
class InvoiceBuilder
def initialize(invoice, employee)
@invoice, @employee = invoice, employee
end
private
attr_reader :invoice, :employee
end
you can just do
class InvoiceBuilder
pattr_initialize :invoice, :employee
end
This nicely complements Ruby's built-in attr_accessor, attr_reader and attr_writer.
Supports positional arguments as well as optional and required hash arguments.
Also provides conveniences for creating value objects, method objects, query methods and abstract methods.
attr_initializer :foo, :bar. Alternative: attr_initialize_method. Rationale for change: I'm not very opposed to the current name, but I think this is more clear. The previous one sounds like it will take some action when you call the metod ("what does it initialize the value to?" I have myself asking). This one is more obvious that it does something regarding the initializer of the class (or constructor if you will, but that's a name Ruby doesn't use).
Defines an initializer that takes two arguments and assigns @foo and @bar.
attr_initialize :foo, [:bar, :baz!] defines an initializer that takes one regular argument, assigning @foo, and one hash argument, assigning @bar (optional) and @baz (required).
attr_initialize [:bar, :baz!] defines an initializer that takes one hash argument, assigning @bar (optional) and @baz (required).
attr_private_reader :foo, :bar. other suggestions: pattr_reader :foo, :bar (and more methods can be added if of any use: pattr_accessors, pattr_writer). Rationale for change: It's very unclear from the current method name attr_private that it only declares a writer. I wouldn't have guessed that...
Defines private readers for @foo and @bar.
attr_value_object :foo, :bar (other suggestions: attr_as_value_object, attr_for_value_object). Rationale for change: Good to have full name of design pattern in name.
Defines public readers. Does not define writers, as value objects are typically immutable.
Defines object equality: two value objects of the same class with the same values are equal.
pattr_initialize :foo, :bar (I'm unsure about the current naming. It's very unclear what it does the first time you see it. However I don't have a single alternative I have decided on - instead I have several ideas. The downside is that they're longer. More verbose: attr_initialize_method_and_private_reader which is not that good. Other ideas that are shorter: pattr_initializer_and_reader, attr_initializer_and_private_reader. I like those names because they're more like Lego - they build upon the previous method names in the gem and you tuck on an and_foo to the declaration in your class as your needs change)
Defines both initializer and private readers: shortcut for
attr_initialize :foo, :bar
attr_private :foo, :bar
The attr_initialize notation for hash arguments is also supported: pattr_initialize :foo, [:bar, :baz!]
vattr_initialize :foo, :bar. (alternative namings: attr_for_value_object_and_initializer, attr_value_object_and_initializer, attr_initializer_and_value_object. Also see the previous method's comments and ideas. A "p" is good for "private", a "v" for value object is a bit more streching it.)
Defines initializer, public readers and value object identity: shortcut for
attr_initialize :foo, :bar
attr_value :foo, :bar
The attr_initialize notation for hash arguments is also supported: vattr_initialize :foo, [:bar, :baz!]
method_object :fooable?, :foo. Good. (Mnemonic rule: argument order is same as order of "method" and "object" in method-name)
Defines a .fooable? class method that takes arguments (foo) and delegates to an instance method that can access those arguments as private readers.
This is useful for method objects:
class PriceCalculator
method_object :calculate,
:order
def calculate
total * factor
end
private
def total
order.items.map(&:price).inject(:+)
end
def factor
1 + rand
end
end
class Order
def price
PriceCalculator.calculate(self)
end
# …
endShortcut for
attr_initialize :foo
attr_private :foo
def self.fooable?(foo)
new(foo).fooable?
endThe attr_initialize notation for hash arguments is also supported: method_object :fooable?, :foo, [:bar, :baz!]
You don't have to specify readers if you don't want them: method_object :fooable? is also valid.
Defines query methods like foo?, which is true if (and only if) foo_id is truthy. Goes well with Active Record.
Defines query methods like foo?, which is true if (and only if) foo is truthy.
attr_implement :foo, :bar. Should be named abstract_method and abstract_methods - has nothing to do with attrs (?).
Defines nullary (0-argument) methods foo and bar that raise e.g. "Implement a 'foo()' method".
attr_implement :foo, [:name, :age] will define a binary (2-argument) method foo that raises "Implement a 'foo(name, age)' method".
This is suitable for abstract methods in base classes, e.g. when using the template method pattern.
Findability is a core value.
Hence the long name attr_initialize, so you see it when scanning for the initializer;
and the enforced questionmarks with attr_id_query :foo?, so you can search for that method.
See: "Struct inheritance is overused"
Instead of attr_private :foo, you could do private; attr_reader :foo.
Other than being more to type, declaring attr_reader after private will actually give you a warning (deserved or not) if you run Ruby with warnings turned on.
If you don't want the dependency on attr_extras, you can get rid of the warnings with attr_reader :foo; private :foo. Or just define a regular private method.
Add this line to your application's Gemfile:
gem "attr_extras"
And then execute:
bundle
Or install it yourself as:
gem install attr_extras
Run then with:
rake
Or to see warnings (try not to have any):
RUBYOPT=-w rake
Copyright (c) 2012-2014 Barsoom AB
MIT License
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.