如何在symfony2捆绑软件中实施策略模式？

Question

Say we have a Symfony bundle that contains a service having a dependency defined by an interface (Strategy pattern). I also have several implementations of the interface (ie. strategies) defined in the same bundle. Each strategy may also have various further dependencies that my require further configuration. So my services.yml in the bundle may look like that:

services:
  my_service:
    class: MyBundle\Services\MyService
    arguments: ['@my_strategy']
  my_strategy_service_1:
    class: MyBundle\Services\MyStrategyService1
  my_strategy_service_2:
    class: MyBundle\Services\MyStrategyService2
    argument: [@my_memcache]

And I can choose the implementation in the config.yml in the application.

services:
  my_strategy:
    alias: my_strategy_service_2
  my_memcache:
    class: Memcached
    calls:
      - [ addServer, [%memcache_host%, %memcache_port%] ]

Let's stick to the example and let's change the implementation. If I write in the config.yml in the application:

services:
  my_strategy:
    alias: my_strategy_service_1

it still, unfortunately requires me to define "my_memcache" service, even if it's not used this time, but only defined in the bundle. How can I deal with the situation? Can I enforce checking the dependencies for "my_strategy_service_2" only if it's really used?

Answer 1

Usually I implement a "register" between context and strategy use:

1. Define all possibile strategies (services) and I tag them
2. Define a register were I have injected all possibile strategies (services) by fetching them through tags (with a compiler pass )
3. Retrieve the strategy through the register (either by a configuration parameter injected or by passing it when calling the function to lookup for correct strategy)
4. Use the strategy

Hope it's clear