attr_extras
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.
Usage
attr_initialize :foo, :bar
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_initialize
can also accept a block which will be invoked after initialization. This is useful for calling super
appropriately in subclasses or initializing private data as necessary.
attr_private :foo, :bar
Defines private readers for @foo
and @bar
.
attr_value :foo, :bar
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
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
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
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
# …
end
Shortcut for
attr_initialize :foo
attr_private :foo
def self.fooable?(foo)
new(foo).fooable?
end
The 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.
attr_id_query :foo?, :bar?
Defines query methods like foo?
, which is true if (and only if) foo_id
is truthy. Goes well with Active Record.
attr_query :foo?, :bar?
Defines query methods like foo?
, which is true if (and only if) foo
is truthy.
attr_implement :foo, :bar
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.
Philosophy
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.
Why not use Struct
?
See: "Struct inheritance is overused"
Why not use private; attr_reader :foo
?
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.
Installation
Add this line to your application's Gemfile
:
gem "attr_extras"
And then execute:
bundle
Or install it yourself as:
gem install attr_extras
Running the tests
Run then with:
rake
Or to see warnings (try not to have any):
RUBYOPT=-w rake
Contributors
License
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.