Ecosyste.ms: Awesome
An open API service indexing awesome lists of open source software.
https://github.com/saturnflyer/surrounded
Create encapsulated systems of objects and focus on their interactions
https://github.com/saturnflyer/surrounded
Last synced: 10 days ago
JSON representation
Create encapsulated systems of objects and focus on their interactions
- Host: GitHub
- URL: https://github.com/saturnflyer/surrounded
- Owner: saturnflyer
- License: mit
- Created: 2013-06-07T02:15:58.000Z (over 11 years ago)
- Default Branch: master
- Last Pushed: 2023-03-08T17:47:25.000Z (over 1 year ago)
- Last Synced: 2024-10-14T16:09:07.962Z (28 days ago)
- Language: Ruby
- Homepage:
- Size: 494 KB
- Stars: 252
- Watchers: 11
- Forks: 14
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: Changelog.md
- License: LICENSE.txt
Awesome Lists containing this project
- awesome-ruby - Surrounded - Encapsulated related objects in a single system to add behavior during runtime. Extensible implementation of DCI. (Abstraction)
README
# 
## Be in control of business logic.
[](https://github.com/saturnflyer/surrounded/actions)
[](https://codeclimate.com/github/saturnflyer/surrounded)
Surrounded is designed to help you better manage your business logic by keeping cohesive behaviors together. Bring objects together to implement your use cases and gain behavior only when necessary.
## How to think about your objects
First, name the problem you're solving. Then, break down your problem into responsible roles.
Use your problem name as a class and extend it with `Surrounded::Context`
It might look like this:
```ruby
class Employment
extend Surrounded::Context
role :boss
role :employee
end
```
In your application, you'll initialize this class with objects to play the roles that you've defined, so you'll need to specify which role players will use which role.
```ruby
class Employment
extend Surrounded::Context
initialize :employee, :boss
role :boss
role :employee
end
```
Here, you've specified the order when initializing so you can use it like this:
```ruby
user1 = User.find(1)
user2 = User.find(2)
context = Employment.new(employee: user1, boss: user2)
```
That ensures that `user1` will become (and have all the features of) the `employee` and `user2` will become (and have all the features of) the `boss`.
There are 2 things left to do:
1. define behaviors for each role and
2. define how you can trigger their actions
Initializing contexts does not require the use of keyword arguments, but you may opt out.
You should consider using explicit names when initializing now by using `initialize_without_keywords`:
```ruby
class Employment
extend Surrounded::Context
initialize_without_keywords :employee, :boss
end
user1 = User.find(1)
user2 = User.find(2)
context = Employment.new(user1, user2)
```
This will allow you to prepare your accessing code to use keywords.
If you need to override the initializer with additional work, you have the ability to use a block to be evaluated in the context of the initialized object.
```ruby
initialize :role1, :role2 do
map_role(:role3, 'SomeRoleConstantName', initialize_the_object_to_play)
end
```
This block will be called _after_ the default initialization is done.
## Defining behaviors for roles
Behaviors for your roles are easily defined just like you define a method. Provide your role a block and define methods there.
```ruby
class Employment
extend Surrounded::Context
initialize :employee, :boss
role :boss
role :employee do
def work_weekend
if fed_up?
quit
else
schedule_weekend_work
end
end
def quit
say("I'm sick of this place, #{boss.name}!")
stomp
throw_papers
say("I quit!")
end
def schedule_weekend_work
# ...
end
end
end
```
If any of your roles don't have special behaviors, like `boss`, you don't need to specify it. Your `initialize` setup will handle assiging who's who when this context is used.
```ruby
class Employment
extend Surrounded::Context
initialize :employee, :boss
role :employee do
#...
end
end
```
## Triggering interactions
You'll need to define way to trigger these behaviors to occur so that you can use them.
```ruby
context = Employment.new(employee: user1, boss: user2)
context.plan_weekend_work
```
The method you need is defined as an instance method in your context, but before that method will work as expected you'll need to mark it as a trigger.
```ruby
class Employment
extend Surrounded::Context
initialize :employee, :boss
def plan_weekend_work
employee.work_weekend
end
trigger :plan_weekend_work
role :employee do
#...
end
end
```
Trigger methods are different from regular instance methods in that they apply behaviors from the roles to the role players.
A regular instance method just does what you define. But a trigger will make your role players come alive with their behaviors.
You may find that the code for your triggers is extremely simple and is merely creating a method to tell a role player what to do. If you find you have many methods like this:
```ruby
def plan_weekend_work
employee.work_weekend
end
trigger :plan_weekend_work
```
You can shorten it to:
```ruby
trigger :plan_weekend_work do
employee.work_weekend
end
```
But it can be even simpler and follows the same pattern provided by Ruby's standard library Forwardable:
```ruby
# The first argument is the role to receive the messaged defined in the second argument.
# The third argument is optional and if provided will be the name of the trigger method on your context instance.
forward_trigger :employee, :work_weekend, :plan_weekend_work
# Alternatively, you can use an API similar to that of the `delegate` method from Forwardable
forwarding [:work_weekend] => :employee
```
The difference between `forward_trigger` and `forwarding` is that the first accepts an alternative method name for the context instance method. There's more on this below in the "Overview in code" section, or see `lib/surrounded/context/forwarding.rb`.
There's one last thing to make this work.
## Getting your role players ready
You'll need to include `Surrounded` in the classes of objects which will be role players in your context.
It's as easy as:
```ruby
class User
include Surrounded
# ...
end
```
This gives each of the objects the ability to understand its context and direct access to other objects in the context.
## Why is this valuable?
By creating environments which encapsulate roles and all necessary behaviors, you will be better able to isolate the logic of your system. A `user` in your system doesn't have all possible behaviors defined in its class, it gains the behaviors only when they are necessary.
The objects that interact have their behaviors defined and available right where they are needed. Implementation is in proximity to necessity. The behaviors you need for each role player are highly cohesive and are coupled to their use rather than being coupled to the class of an object which might use them at some point.
# Deeper Dive
## Create encapsulated environments for your objects.
Typical initialization of an environment, or a Context in DCI, has a lot of code. For example:
```ruby
class Employment
attr_reader :employee, :boss
private :employee, :boss
def initialize(employee, boss)
@employee = employee.extend(Employee)
@boss = boss
end
module Employee
# extra behavior here...
end
end
```
This code allows the Employment class to create instances where it will have an `employee` and a `boss` role internally. These are set to `attr_reader`s and are made private.
The `employee` is extended with behaviors defined in the `Employee` module, and in this case there's no extra stuff for the `boss` so it doesn't get extended with anything.
Most of the time you'll follow a pattern like this. Some objects will get extra behavior and some won't. The modules that you use to provide the behavior will match the names you use for the roles to which you assign objects.
By adding `Surrounded::Context` you can shortcut all this work.
```ruby
class Employment
extend Surrounded::Context
initialize(:employee, :boss)
module Employee
# extra behavior here...
end
end
```
Surrounded gives you an `initialize` class method which does all the setup work for you.
## Managing Roles
_I don't want to use modules. Can't I use something like SimpleDelegator?_
Well, it just so happens that you can. This code will work just fine:
```ruby
class Employment
extend Surrounded::Context
initialize(:employee, :boss)
class Employee < SimpleDelegator
# extra behavior here...
end
end
```
Instead of extending the `employee` object, Surrounded will run `Employee.new(employee)` to create the wrapper for you. You'll need to include the `Surrounded` module in your wrapper, but we'll get to that.
But the syntax can be even simpler than that if you want.
```ruby
class Employment
extend Surrounded::Context
initialize(:employee, :boss)
role :employee do
# extra behavior here...
end
end
```
By default, this code will create a module for you named `Employee`. If you want to use a wrapper, you can do this:
```ruby
class Employment
extend Surrounded::Context
initialize(:employee, :boss)
wrap :employee do
# extra behavior here...
end
end
```
But if you're making changes and you decide to move from a module to a wrapper or from a wrapper to a module, you'll need to change that method call. Instead, you could just tell it which type of role to use:
```ruby
class Employment
extend Surrounded::Context
initialize(:employee, :boss)
role :employee, :wrapper do
# extra behavior here...
end
end
```
The default available types are `:module`, `:wrap` or `:wrapper`, and `:interface`. We'll get to `interface` below. The `:wrap` and `:wrapper` types are the same and they'll both create classes which inherit from SimpleDelegator _and_ include Surrounded for you.
These are minor little changes which highlight how simple it is to use Surrounded.
_Well... I want to use [Casting](https://github.com/saturnflyer/casting) so I get the benefit of modules without extending objects. Can I do that?_
Yup. The ability to use Casting is built-in. If the objects you provide to your context respond to `cast_as` then Surrounded will use that.
_Ok. So is that it?_
There's a lot more. Let's look at the individual objects and what they need for this to be valuable...
## Objects' access to their environments
Add `Surrounded` to your objects to give them awareness of other objects.
```ruby
class User
include Surrounded
end
```
Now the `User` instances will be able to implicitly access objects in their environment.
Via `method_missing` those `User` instances can access a `context` object it stores in an internal collection.
Inside of the `Employment` context we saw above, the `employee` and `boss` objects are instances of `User` for this example.
Because the `User` class includes `Surrounded`, the instances of that class will be able to access other objects in the same context implicitly.
Let's make our context look like this:
```ruby
class Employment
# other stuff from above is still here...
def plan_weekend_work
employee.quit
end
role :employee do
def quit
say("I'm sick of this place, #{boss.name}!")
stomp
throw_papers
say("I quit!")
end
end
end
```
What's happening in there is that when the `plan_weekend_work` method is called on the instance of `Employment`, the `employee` has the ability to refer to `boss` because it is in the same context, e.g. the same environment.
The behavior defined in the `Employee` module assumes that it may access other objects in it's local environment. The `boss` object, for example, is never explicitly passed in as an argument.
What `Surrounded` does for us is to make the relationship between objects and gives them the ability to access each other. Adding new or different roles to the context now only requires that we add them to the context and nothing else. No explicit references must be passed to each individual method. The objects are aware of the other objects around them and can refer to them by their role name.
I didn't mention how the context is set, however.
## Tying objects together
Your context will have methods of it's own which will trigger actions on the objects inside, but we need those trigger methods to set the accessible context for each of the contained objects.
Here's an example of what we want:
```ruby
class Employment
# other stuff from above is still here...
def plan_weekend_work
employee.store_context(self)
employee.quit
employee.remove_context
end
role :employee do
def quit
say("I'm sick of this place, #{boss.name}!")
stomp
throw_papers
say("I quit!")
end
end
end
```
Now that the `employee` has a reference to the context, it won't blow up when it hits `boss` inside that `quit` method.
We saw how we were able to clear up a lot of that repetitive work with the `initialize` method, so this is how we do it here:
```ruby
class Employment
# other stuff from above is still here...
trigger :plan_weekend_work do
employee.quit
end
role :employee do
def quit
say("I'm sick of this place, #{boss.name}!")
stomp
throw_papers
say("I quit!")
end
end
end
```
By using this `trigger` keyword, our block is the code we care about, but internally the method is created to first set all the objects' current contexts.
The context will also store the triggers so that you can, for example, provide details outside of the environment about what triggers exist.
```ruby
context = Employment.new(current_user, the_boss)
context.triggers #=> [:plan_weekend_work]
```
You might find that useful for dynamically defining user interfaces.
Sometimes I'd rather not use this DSL, however. I want to just write regular methods.
We can do that too. You'll need to opt in to this by specifying `trigger :your_method_name` for the methods you want to use.
```ruby
class Employment
# other stuff from above is still here...
def plan_weekend_work
employee.quit
end
trigger :plan_weekend_work
# or in Ruby 2.x
trigger def plan_weekend_work
employee.quit
end
role :employee do
def quit
say("I'm sick of this place, #{boss.name}!")
stomp
throw_papers
say("I quit!")
end
end
end
```
This will allow you to write methods like you normally would. They are aliased internally with a prefix and the method name that you use is rewritten to add and remove the context for the objects in this context. The public API of your class remains the same, but the extra feature of wrapping your method is handled for you.
This works like Ruby's `public`,`protected`, and `private` keywords in that you can send symbols of method names to it. But `trigger` does not alter the parsing of the document like those core keywords do. In other words, you can't merely type `trigger` on one line, and have methods added afterward be treated as trigger methods.
## Access Control / Permissions for Triggers
If you decide to build a user interface from the available triggers, you'll find you need to know what triggers are available.
Fortunately, you can make it easy.
By running `protect_triggers` you'll be able to define when triggers may or may not be run. You can still run them, but they'll raise an error. Here's an example.
```ruby
class Employment
extend Surrounded::Context
protect_triggers
def plan_weekend_work
employee.quit
end
trigger :plan_weekend_work
disallow :plan_weekend_work do
employee.bank_balance > 1000000
end
end
```
Then, when the employee role's `bank_balance` is greater than `1000000`, the available triggers won't include `:plan_weekend_work`.
You can compare the instance of the context by listing `all_triggers` and `triggers` to see what could be possible and what's currently possible.
Alternatively, if you just want to define your own methods without the DSL using `disallow`, you can just follow the pattern of `disallow_#{method_name}?` when creating your own protection.
In fact, that's exactly what happens with the `disallow` keyword. After using it here, we'd have a `disallow_plan_weekend_work?` method defined.
If you call the disallowed trigger directly, you'll raise an `Employment::AccessError` exception and the code in your trigger will not be run. You may rescue from that or you may rescue from `Surrounded::Context::AccessError` although you should prefer to use the error name from your own class.
## Restricting return values
_Tell, Don't Ask_ style programming can better be enforced by following East-oriented Code principles. This means that the return values from methods on your objects should not provide information about their internal state. Instead of returning values, you can enforce that triggers return the context object. This forces you to place context responsiblities inside the context and prevents leaking the details and responsiblities outside of the system.
Here's how you enforce it:
```ruby
class Employment
extend Surrounded::Context
east_oriented_triggers
end
```
That's it.
With that change, any trigger you define will execute the block you provide and return `self`, being the instance of the context.
## Where roles exist
By using `Surrounded::Context` you are declaring a relationship between the objects inside playing your defined roles.
Because all the behavior is defined internally and only relevant internally, those relationships don't exist outside of the environment.
Surrounded makes all of your role modules and classes private constants. It's not a good idea to try to reuse behavior defined for one context in another area.
## The role DSL
Using the `role` method to define modules and classes takes care of the setup for you. This way you can swap between implementations:
```ruby
# this uses modules which include Surrounded
role :source do
def transfer
self.balance -= amount
destination.balance += amount
self
end
end
# this uses SimpleDelegator and Surrounded
role :source, :wrap do
def transfer
self.balance -= amount
destination.balance += amount
__getobj__
end
end
# this uses a special interface object which pulls
# methods from a module and applies them to your object.
role :source, :interface do
def transfer
self.balance -= amount
# not able to access destination unless the object playing source is Surrounded
destination.balance += amount
self
end
end
```
The `:interface` option is a special object which has all of the standard Object methods removed (excepting ones like `__send__` and `object_id`) so that other methods will be pulled from the ones that you define, or from the object it attempts to proxy.
Notice that the `:interface` allows you to return `self` whereas the `:wrap` acts more like a wrapper and forces you to deal with that shortcoming by using it's wrapped-object-accessor method: `__getobj__`.
The downside of using an interface is that it is still a wrapper and it only has access to the other objects in the context if the wrapped object already includes Surrounded. All of your defined role methods are executed in the context of the object playing the role, but the interface has it's own identity.
If you'd like to choose one and use it all the time, you can set the default:
```ruby
class MoneyTransfer
extend Surrounded::Context
self.default_role_type = :interface # also :wrap, :wrapper, or :module
role :source do
def transfer
self.balance -= amount
destination.balance += amount
self
end
end
end
```
Or, if you like, you can choose the default for your entire project:
```ruby
Surrounded::Context.default_role_type = :interface
class MoneyTransfer
extend Surrounded::Context
role :source do
def transfer
self.balance -= amount
destination.balance += amount
self
end
end
end
```
## Working with collections
If you want to use an Array of objects (for example) as a role player in your context,
you may do so. If you want each item in your collection to gain behavior, you merely need to
create a role for the items.
Surrounded will attempt to guess at the singular role name. For example, a role player named `members` would
be given the behaviors from a `Members` behavior module or class. Each item in your `members` collection
would be given behavior from a `Member` behavior module or class if you create one.
```ruby
class Organization
extend Surrounded::Context
initialize_without_keywords :leader, :members
role :members do
# special behavior for the collection
end
role :member do
# special behavior to be applied to each member in the collection
end
end
```
If you want to change the way the singular verson of a role is used, override `singularize_name`:
```ruby
class Organization
extend Surrounded::Context
def singularize_name(name)
if name == "my special rule"
# do your thing
else
super # use the default
end
end
end
```
## Reusing context objects
If you create a context object and need to use the same type of object with new role players, you may use the `rebind` method. It will clear any instance_variables from your context object and map the given objects to their names:
```ruby
context = Employment.new(employee: current_user, boss: the_boss)
context.rebind(employee: another_user, boss: someone_else) # same context, new players
```
## Background Processing
While there's no specific support for background processing, your context objects make it easy for you to add your own by remembering what arguments were provided during initialization.
When you initialize a context, it will keep track of the parameters and their matching arguments in a private hash called `initializer_arguments`. This allows you to write methods to create a context object and have itself sent to a background processor.
```ruby
class ExpensiveCalculation
extend Surrounded::Context
initialize :leader, :members
def send_to_background(trigger_method)
background_arguments = initializer_arguments.merge(trigger: trigger_method)
BackgroundProcessor.enqueue(self.class.name, **background_arguments)
end
class BackgroundProcessor
def perform(**args)
trigger_name = args.delete(:trigger)
job_class.new(args).send(trigger_name)
end
end
end
ExpensiveCalculation.new(leader: some_object, members: some_collection).send_to_background(:do_expensive_calculation)
```
The above example is merely pseudo-code to show how `initializer_arguments` can be used. Customize it according to your own needs.
## Overview in code
Here's a view of the possibilities in code.
```ruby
# set default role type for *all* contexts in your program
Surrounded::Context.default_role_type = :module # also :wrap, :wrapper, or :interface
class ActiviatingAccount
extend Surrounded::Context
# set the default role type only for this class
self.default_role_type = :module # also :wrap, :wrapper, or :interface
# shortcut initialization code
initialize(:activator, :account)
# or handle it yourself
def initialize(activator:, account:)
# this must be done to handle the mapping of roles to objects
# pass an array of arrays with role name symbol and the object for that role
map_roles([[:activator, activator],[:account, account]])
# or pass a hash
map_roles(:activator => activator, :account => account)
# or load extra objects, perform other functions, etc. if you need and then use super
account.perform_some_funtion
super
end
# these also must be done if you create your own initialize method.
# this is a shortcut for using attr_reader and private
private_attr_reader :activator, :account
# If you need to mix default initialzation and extra work use a block
initialize :activator, :account do
map_roles(:third_party => get_some_other_object)
# explicitly set a single role
map_role(:something_new, 'SomeRoleConstant', object_to_play_the_role)
end
# but remember to set the extra accessors:
private_attr_reader :third_party, :something_new
# initialize without keyword arguments
initialize_without_keywords(:activator, :account)
# this makes the following instance method signature with positional arguments
def initialize(activator, account)
# ...
end
# Handle method name collisions on role players against role names in the context
on_name_collision :raise # will raise your context namespaced error: ActiviatingAccount::NameCollisionError
on_name_collision :warn
on_name_collision ->(message){ puts "Here's the message! #{message}" }
on_name_collision :my_custom_handler
def my_custom_handler(message)
# do something with the message here
end
role :activator do # module by default
def some_behavior; end
end
# role_methods :activator, :module do # alternatively use role_methods if you choose
# def some_behavior; end
# end
#
# role :activator, :wrap do
# def some_behavior; end
# end
#
# role :activator, :interface do
# def some_behavior; end
# end
#
# use your own classes if you don't want SimpleDelegator
# class SomeSpecialRole
# include Surrounded # <-- you must remember this in your own classes
# # Surrounded assumes SomeSpecialRole.new(some_special_role)
# def initialize(...);
# # ... your code here
# end
# end
# if you use a regular method and want to use context-specific behavior,
# you must handle storing the context yourself:
def regular_method
apply_behaviors # handles the adding of all the roles and behaviors
activator.some_behavior # behavior not available unless you apply roles on initialize
ensure
# Use ensure to enforce the removal of behaviors in case of exceptions.
# This also does not affect the return value of this method.
remove_behaviors # handles the removal of all roles and behaviors
end
# This trigger or the forward* methods are preferred for creating triggers.
trigger :some_trigger_method do
activator.some_behavior # behavior always available
end
trigger def some_other_trigger
activator.some_behavior # behavior always available
end
def regular_non_trigger
activator.some_behavior # behavior always available with the following line
end
trigger :regular_non_trigger # turns the method into a trigger
# create restrictions on what triggers may be used
protect_triggers # <-- this is required if you want to protect your triggers this way.
disallow :some_trigger_method do
# whatever conditional code for the instance of the context
end
# you could also use `guard` instead of `disallow`
# or define your own method without the `disallow` keyword
def disallow_some_trigger_method?
# whatever conditional code for the instance of the context
end
# Prefer using `disallow` because it will wrap role players in their roles for you;
# the `disallow_some_trigger_method?` defined above, does not.
# Create shortcuts for triggers as class methods
# so you can do ActiviatingAccount.some_trigger_method(activator, account)
# This will make all triggers shortcuts.
shortcut_triggers
# Alterantively, you could implement shortcuts individually:
def self.some_trigger_method(activator, account)
instance = self.new(activator, account)
instance.some_trigger_method
end
# Set triggers to always return the context object
# so you can enforce East-oriented style or Tell, Don't Ask
east_oriented_triggers
# Forward context instance methods as triggers to role players
forward_trigger :role_name, :method_name
forward_trigger :role_name, :method_name, :alternative_trigger_name_for_method_name
forward_triggers :role_name, :list, :of, :methods, :to, :forward
forwarding [:list, :of, :methods, :to, :forward] => :role_name
end
# with initialize (also keyword_initialize)
context = ActiviatingAccount.new(activator: some_object, account: some_account)
# with initialize_without_keywords
context = ActiviatingAccount.new(some_object, some_account)
context.triggers # => lists a Set of triggers
# when using protect_triggers
context.triggers # => lists a Set of triggers which may currently be called
context.all_triggers # => lists a Set of all triggers (the same as if protect_triggers was _not_ used)
context.allow?(:trigger_name) # => returns a boolean if the trigger may be run
# reuse the context object with new role players
context.rebind(activator: another_object, account: another_account)
```
## Dependencies
The dependencies are minimal. The plan is to keep it that way but allow you to configure things as you need. The [Triad](http://github.com/saturnflyer/triad) project was written specifically to manage the mapping of roles and objects to the modules which contain the behaviors. It is used in Surrounded to keep track of role player, roles, and role constant names but it is not a hard requirement. You may implement your own but presently you'll need to dive into the implementation to fully understand how. Future updates may provide better support and guidance.
If you want to override the class used for mapping roles to behaviors, override the `role_map` method.
```ruby
class MyContext
extend Surrounded::Context
def role_map
@container ||= role_mapper_class.new(base: MySpecialDataContainer)
end
end
```
The class you provide will be initialized with `new` and is expected to implement the methods: `:update`, `:each`, `:values`, and `:keys`.
If you're using [Casting](http://github.com/saturnflyer/casting), for example, Surrounded will attempt to use that before extending an object, but it will still work without it.
## Support for other ways to apply behavior
Surrounded is designed to be flexible for you. If you have your own code to manage applying behaviors, you can setup your context class to use it.
### Additional libraries
Here's an example using [Behavioral](https://github.com/saturnflyer/behavioral)
```ruby
class MyCustomContext
extend Surrounded::Context
initialize :employee, :boss
def module_extension_methods
[:with_behaviors].concat(super)
end
def module_removal_methods
[:without_behaviors].concat(super)
end
end
```
If you're using your own non-SimpleDelegator wrapper you can conform to that; whatever it may be.
```ruby
class MyCustomContext
extend Surrounded::Context
initialize :employee, :boss
class Employee < SuperWrapper
include Surrounded
# defined behaviors here...
def wrapped_object
# return the object that is wrapped
end
end
def unwrap_methods
[:wrapped_object]
end
end
```
### Applying individual roles
If you'd like to use a special approach for just a single role, you may do that too.
When applying behaviors from a role to your role players, your Surrounded context will first look for a method named `"apply_behavior_#{role}"`. Define your own method and set it to accept 2 arguments: the role constant and the role player.
```ruby
class MyCustomContext
extend Surrounded::Context
initialize :employee, :boss
def apply_behavior_employee(behavior_constant, role_player)
behavior_constant.build(role_player).apply # or whatever your need to do with your constant and object.
end
end
```
You can also plan for special ways to remove behavior as well.
```ruby
class MyCustomContext
extend Surrounded::Context
initialize :employee, :boss
def remove_behavior_employee(behavior_constant, role_player)
role_player.cleanup # or whatever your need to do with your constant and object.
end
end
```
You can remember the method name by the convention that `remove` or `apply` describes it's function, `behavior` refers to the first argument (the constant holding the behaviors), and then the name of the role which refers to the role playing object: `remove_behavior_role`.
## Name collisions between methods and roles
Lets say that you wish to create a context as below, intending to use instances of the following two classes as role players:
```ruby
class Postcode
# other methods...
def code
@code
end
def country
@country
end
end
class Country
# other methods...
def country_code
@code
end
end
class SendAParcel
extend Surrounded::Context
keyword_initialize :postcode, :country
trigger :send do
postcode.send
end
role :postcode do
def send
# do things...
country_code = country.country_code # name collision...probably raises an exception!
end
end
end
```
When you call the `:send` trigger you are likely to be greeted with an `NoMethodError` exception. The reason for this is that there is a name collision between `Postcode#country`, and the `:country` role in the `SendAParcel` context. Where a name collision exists, the method in the role player overrides that of the calling class and you get unexpected results.
To address this issue, use `on_name_collision` to specify the name of a method to use when collisions are found:
```ruby
class SendAParcel
extend Surrounded::Context
on_name_collision :raise
end
```
This option will raise an exception (obviously). You may use any method which is available to the context but it must accept a single message as the argument.
You can also use a lambda:
```ruby
class SendAParcel
extend Surrounded::Context
on_name_collision ->(message){ puts "Here's the message: #{message}"}
end
```
You may also user a class method:
```ruby
class SendAParcel
extend Surrounded::Context
def self.handle_collisions(message)
Logger.debug "#{Time.now}: #{message}"
end
end
```
## How to read this code
If you use this library, it's important to understand it.
As much as possible, when you use the Surrounded DSL for creating triggers, roles, initialize methods, and others you'll likely find the actual method definitions created in a module and then find that module included in your class.
This is a design choice which allows you to override any standard behavior more easily.
### Where methods exist and why
When you define an initialize method for a Context class, Surrounded _could_ define the method on your class like this:
```ruby
def initialize(*roles)
self.class_eval do # <=== this evaluates on _your_ class and defines it there.
# code...
end
end
```
If we used the above approach, you'd need to redefine initialize in its entirety:
```ruby
initialize(:role1, role2)
def initialize(role1, role2) # <=== this will completely redefine initialize on _this class_
super # <=== this will NOT be the initialize method as provided to the Surrounded initialize above.
end
```
Surrounded uses a more flexible approach for you:
```ruby
def initialize(*roles)
mod = Module.new
mod.class_eval do # <=== this evaluates on the module and defines it there.
# code...
end
include mod # <=== this adds it to the class ancestors
end
```
With this approach you can use the way Surrounded is setup, but make changes if you need.
```ruby
initialize(:role1, :role2) # <=== defined in a module in the class ancestors
def initialize(role1, role2)
super # <=== run the method as defined above in the Surrounded DSL
# ... then do additional work
end
```
### Read methods, expect modules
When you go to read the code, expect to find behavior defined in modules.
## Installation
Add this line to your application's Gemfile:
```ruby
gem 'surrounded'
```
And then execute:
$ bundle
Or install it yourself as:
$ gem install surrounded
## Installation for Rails
See [surrounded-rails](https://github.com/saturnflyer/surrounded-rails)
## Contributing
1. Fork it
2. Create your feature branch (`git checkout -b my-new-feature`)
3. Commit your changes (`git commit -am 'Add some feature'`)
4. Push to the branch (`git push origin my-new-feature`)
5. Create new Pull Request