Assembly overrides provide a way to configure or customize an Assembly when constructing an instance.

For example, using the assembly created above, one might want to change the IO object logged to.

The simplest way to do this is to provide a hash which will override values in the assembly (as if the set command was called in the DSL):

require 'stringio'
io = StringIO.new
instance = assembly.new log_io: io
instance.util.logger.info "test"
puts(io.string.match(/INFO -- : test/) != nil)

# output: true

The limitation of this is that it can only override basic values. To override more complex elements a block can be given to new allowing the full assembly DSL.

class MyLogger
  def initialize(io)
    @io = io
  def info(msg)
    @io.puts "INFO #{msg}"

instance = assembly.new do
  group :util do
    service :logger do
      MyLogger.new original.log_io
instance.util.logger.info "test"

# output: INFO test

One thing of note is that elements from the assembly are accessible in overrides via the original method, as seen above. This can also be used to access the original versions of elements that have been overridden.

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