Feature #4862: Struct#to_hash

• Status: Rejected
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[postmodern (Hal Brodigan)]

Occasionally, it is necessary to convert a Struct to a Hash (especially when generating JSON from an Array of Structs). A Struct#to_hash method would be very useful in this situation.

class Struct

  #
  # Returns the Hash representation of the members and values within the struct.
  #
  def to_hash
    new_hash = {}

    each_pair do |member,value|
      new_hash[member] = value
    end

    new_hash
  end

end

[rossmeissl (Andy Rossmeissl)]

def to_hash() Hash[members.zip(values)] end

[trans (Thomas Sawyer)]

A Struct doesn't respond to hardly any Hash methods in general. So #to_h seems more appropriate.

[trans (Thomas Sawyer)]

Then again maybe I'm wrong b/c I was just surprised by the fact that a Struct doesn't have (or at least act like it has) instance_variables.

Struct.new(:a).new(1).instance_variables #=> []

[Eregon (Benoit Daloze)]

Thomas Sawyer wrote:

Then again maybe I'm wrong b/c I was just surprised by the fact that a Struct doesn't have (or at least act like it has) instance_variables.

Struct.new(:a).new(1).instance_variables #=> []

Yeah, it is implemented with an array stored in the RStruct struct in MRI.

A Struct#to_hash method would be very useful in this situation.

I agree.

#to_hash is the right method name because there is no #to_h (but indeed it is somewhat inconsistent with #to_i, #to_int, ...)

[trans (Thomas Sawyer)]

Despite it's implementation, I thought Struct was intended to provide a convenient way to make quick classes. Which is why I assume it would have instance variables. I can understand though that it would be implemented in another fashion for speed. But I would still think the public interface to appear as if it were a typical sort of class.

Given it's current interface it hardly resembles a Hash at all. I think #each at least should act the same as a Hash if #to_hash would be added to it, but instead it acts like an Array:

s = Struct.new(:a, :b).new(1,2)
=> #
s.map{ |a| a }
=> [1, 2]

"because there is no #to_h (but indeed it is somewhat inconsistent with #to_i, #to_int, ...)"

Not just "somewhat". So I ignore all that heehawing and define #to_h wherever it makes sense when I need it. Why #to_h should be carved out as some odd exception seems to me just a lot of needless fuss over... what?

[drbrain (Eric Hodel)]

Struct does use instance variables, you just can't see them from ruby because they don't start with @

[mame (Yusuke Endoh)]

• Status changed from Open to Assigned
• Assignee set to matz (Yukihiro Matsumoto)

[matz (Yukihiro Matsumoto)]

• Status changed from Assigned to Rejected

#to_hash protocol expects the object to be hash-compatible. Struct is not the case.

Matz.