Feature #15222: Add a way to distinguish between Struct classes with and without keyword initializer

• Status: Open
• Assignee: -
• Target version: -

[pluff (Pavel Shutsin)]

With Ruby 2.5.0 Struct subclasses can have different initialize arguments list based on keyword_init option. However, there is no way in Ruby to distinguish Structs with keyword arguments syntax and without.

I propose a class method keyword_init? that will allow developers to understand if given structure has keyword based initializer or not.

Example use case for serialization:

Foo = Struct.new(:foo, keyword_init: true)
Bar = Struct.new(:bar)

def dump_and_load_struct(object)
  serialized = object.to_h
  object.class.new(object.class.keyword_init? ? serialized : serialized.values)
end

dump_and_load_struct(Foo.new(foo: 1)) # #<struct Foo foo=1>
dump_and_load_struct(Bar.new(2)) # #<struct Bar bar=1>

An issue that might be related: https://bugs.ruby-lang.org/issues/14314

[k0kubun (Takashi Kokubun)]

• Related to Bug #14314: Marshalling broken in Ruby 2.5.0 for Structs with keyword_init: true added

[k0kubun (Takashi Kokubun)]

• Related to deleted (Bug #14314: Marshalling broken in Ruby 2.5.0 for Structs with keyword_init: true)

[k0kubun (Takashi Kokubun)]

• Related to Feature #11925: Struct construction with kwargs added

[k0kubun (Takashi Kokubun)]

This would be helpful for implementing custom deserializer of Struct.

Note: If you need to support Ruby 2.5, you would need to do object.class.inspect.end_with?('(keyword_init: true)').