class ActiveSupport::Callbacks::CallTemplate

def expand(target, value, block)

call stack pollution.
The actual invocation is left up to the caller to minimize

target.send(method, *arguments, &block)

This array can be used as such:

[target, block, method, *arguments]

Returns an array of the form:

input values.
Return the parts needed to make this call, with the given 
def expand(target, value, block)
  result = @arguments.map { |arg|
    case arg
    when :value; value
    when :target; target
    when :block; block || raise(ArgumentError)
    end
  }
  result.unshift @method_name
  result.unshift @override_block || block
  result.unshift @override_target || target
  # target, block, method, *arguments = result
  # target.send(method, *arguments, &block)
  result
end