Implementation of loggable struct using Ruby refinements

Require the basic file loggable_struct somewhere:

require "loggable_struct"

And then add to module where you want to have logging:

using LoggableStruct

require_relative "lib/loggable_struct"

SomeStruct = Struct.new :foo, :bar
struct1 = SomeStruct.new foo: 1

begin
  using LoggableStruct
  
  SomeStruct.new.foo
  struct1.foo
end

Output:

I, [2015-05-19T11:50:22.000680 #53964]  INFO -- : :foo
I, [2015-05-19T11:50:22.000790 #53964]  INFO -- : :foo

There are few implementation limitations due to refinements implementation:

• As I mentioned above, monkey patching objects is not supported;
• If you create a new Struct class(not object) inside the block where using LoggableStruct was used, it’s instances will not have their new methods logged.

Both cases are described in specs.

There are few things to mention:

• I tried a few AOP gems and found no one working correctly with refinements;
• Creating Struct descendants does not call inherited method, so I was unable to track descendants this way;
• It still requires monkey-patching for Struct outside of the refinement to track its descendants and their methods;
• Even refinement creates a module, this module doesn’t call neither included nor extended when using is called;
• Using ObjectSpace.each_object allows using this refinement even if loggable_struct and core_ext/struct were included far from the start of the application(e.g. in the middle of the irb or pry session), also it was the cheapest way to track all existing descendants of Struct due to all these limitations.