Feature #18008: `keyword_init?` method for Struct

• Status: Closed
• Assignee: -
• Target version: -

[hkdnet (Ko Sato)]

I'd like to know whether my struct was initialized with keyword_init: true or not.
This information is useful when writing a deserializer (attached an example below).

S1 = Struct.new(:a, :b, keyword_init: true)
S2 = Struct.new(:a, :b)

# Specialized for Struct
def serialize(d)
  d.to_h.merge(__class_name: d.class.name)
end

def deserialize(h)
  klass = Object.const_get(h.delete(:__class_name))
  if keyword_init?(klass)
    # If the class is created with keyword_init: true, the parameter should be passed as keywords
    klass.new(**h)
  else
    # Otherwise, each values are passed in the order of members.
    klass.new(*klass.members.map { |sym| h[sym] })
  end
end

def keyword_init?(klass)
  # I don't want to do this...
  # klass.keyword_init? looks cool. 
  klass.inspect.end_with?('(keyword_init: true)')
end

s1 = S1.new(a: 1, b: 2)

p s1
p s1_ = deserialize(serialize(s1))
p s1 == s1_

s2 = S2.new(1, 2)

p s2
p s2_ = deserialize(serialize(s2))
p s2 == s2_

[k0kubun (Takashi Kokubun)]

+1. While we aim to obviate keyword_init in [Feature #16806], unless we also intend to deprecate the option (for now we don't), we'd need to have the check to correctly write a deserializer of Structs.

[matz (Yukihiro Matsumoto)]

Accepted.

Matz.

[naruse (Yui NARUSE)]

hkdnet's patch is https://github.com/ruby/ruby/pull/4609

[hkdnet (Ko Sato)]

• Status changed from Open to Closed

Applied in changeset git|1a637544166eca6b917fb6f32baeb771f4914b7a.

---

struct.c: Add keyword_init? singleton method for StructClass (#4609)

Fixes [Feature #18008]