Class: Dim::Container

Inherits:
Object
  • Object
show all
Defined in:
lib/dim.rb

Overview

Dim::Container is the central data store for registering services used for dependency injuction. Users register services by providing a name and a block used to create the service. Services may be retrieved by asking for them by name (via the [] operator) or by selector (via the method_missing technique).

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(parent = nil) ⇒ Container

Create a dependency injection container. Specify a parent container to use as a fallback for service lookup.



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# File 'lib/dim.rb', line 51

def initialize(parent=nil)
  @services = {}
  @cache = {}
  @parent = parent || Container
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(sym, *args, &block) ⇒ Object

Lookup a service by message selector. A service with the same name as sym will be returned, or an exception is thrown if no matching service is found.



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# File 'lib/dim.rb', line 89

def method_missing(sym, *args, &block)
  self[sym]
end

Instance Attribute Details

#parent ⇒ Object (readonly)

Returns the value of attribute parent.



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# File 'lib/dim.rb', line 47

def parent
  @parent
end

Class Method Details

.service_block(name) ⇒ Object

Searching for a service block only reaches the Container class when all the containers in the hierarchy search chain have no entry for the service. In this case, the only thing to do is signal a failure.



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# File 'lib/dim.rb', line 104

def self.service_block(name)
  fail(MissingServiceError, "Unknown Service '#{name}'")
end

Instance Method Details

#[](name) ⇒ Object

Lookup a service by name. Throw an exception if no service is found.



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# File 'lib/dim.rb', line 82

def [](name)
  @cache[name] ||= service_block(name).call(self)
end

#register(name, &block) ⇒ Object

Register a service named name. The block will be used to create the service on demand. It is recommended that symbols be used as the name of a service.



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# File 'lib/dim.rb', line 60

def register(name, &block)
  if @services[name]
    fail DuplicateServiceError, "Duplicate Service Name '#{name}'"
  end
  @services[name] = block
end

#register_env(name) ⇒ Object

Lookup a service from ENV variables; fall back to searching the container and its parents for a default value



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# File 'lib/dim.rb', line 68

def register_env(name)
  if value = ENV[name.to_s.upcase]
    register(name) { value }
  else
    begin
      @parent.service_block(name)
    rescue MissingServiceError
      raise EnvironmentVariableNotFound, "Could not find an ENV variable named #{name.to_s.upcase} nor could we find a service named #{name} in the parent container"
    end
  end
end

#service_block(name) ⇒ Object

Return the block that creates the named service. Throw an exception if no service creation block of the given name can be found in the container or its parents.



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# File 'lib/dim.rb', line 96

def service_block(name)
  @services[name] || @parent.service_block(name)
end