Decorators

Decorators wrap existing services to add behavior:

services:
  logger:
    constructor:
      func: "log.New"

  logging_decorator:
    constructor:
      func: "log.NewDecorator"
      args:
        - "@.inner"  # Receives the decorated service
    decorates: logger
    decoration_priority: 10

  metrics_decorator:
    constructor:
      func: "metrics.NewDecorator"
      args:
        - "@.inner"
    decorates: logger
    decoration_priority: 20  # Higher priority wraps first

Execution order: metrics(logging(logger))

Rules

• Must use @.inner in constructor args to receive the decorated service
• Multiple decorators on same service are ordered by decoration_priority (descending)
• The decorated service’s own ID becomes an alias to the outermost decorator, so @logger resolves to metrics(logging(logger))
• The original definition is moved to <decorator>.inner, which @.inner points at (the .inner suffix is reserved and cannot be used in service IDs)
• The decorator type must be compatible with the decorated service type
• The base service and each decorator keep their own shared setting: a shared service may be wrapped by a non-shared decorator and vice versa
• The decorator does not inherit tags of the decorated base service. Tags declared on the base stay on its inner, undecorated definition, so tagged collections receive the undecorated instance (Symfony semantics) — tag the decorator explicitly if the collection should get the decorated one
• A decorator cannot itself be decorated