Class: OpenStruct

Inherits:
Object
  • Object
show all
Defined in:
lib/ostruct.rb

Overview

An OpenStruct is a data structure, similar to a Hash, that allows the definition of arbitrary attributes with their accompanying values. This is accomplished by using Ruby's metaprogramming to define methods on the class itself.

Examples

require "ostruct"

person = OpenStruct.new
person.name = "John Smith"
person.age  = 70

person.name      # => "John Smith"
person.age       # => 70
person.address   # => nil

An OpenStruct employs a Hash internally to store the attributes and values and can even be initialized with one:

australia = OpenStruct.new(:country => "Australia", :capital => "Canberra")
  # => #<OpenStruct country="Australia", capital="Canberra">

Hash keys with spaces or characters that could normally not be used for method calls (e.g. ()[]*) will not be immediately available on the OpenStruct object as a method for retrieval or assignment, but can still be reached through the Object#send method or using [].

measurements = OpenStruct.new("length (in inches)" => 24)
measurements[:"length (in inches)"]       # => 24
measurements.send("length (in inches)")   # => 24

message = OpenStruct.new(:queued? => true)
message.queued?                           # => true
message.send("queued?=", false)
message.queued?                           # => false

Removing the presence of an attribute requires the execution of the delete_field method as setting the property value to nil will not remove the attribute.

first_pet  = OpenStruct.new(:name => "Rowdy", :owner => "John Smith")
second_pet = OpenStruct.new(:name => "Rowdy")

first_pet.owner = nil
first_pet                 # => #<OpenStruct name="Rowdy", owner=nil>
first_pet == second_pet   # => false

first_pet.delete_field(:owner)
first_pet                 # => #<OpenStruct name="Rowdy">
first_pet == second_pet   # => true

Ractor compatibility: A frozen OpenStruct with shareable values is itself shareable.

Caveats

An OpenStruct utilizes Ruby's method lookup structure to find and define the necessary methods for properties. This is accomplished through the methods method_missing and define_singleton_method.

This should be a consideration if there is a concern about the performance of the objects that are created, as there is much more overhead in the setting of these properties compared to using a Hash or a Struct. Creating an open struct from a small Hash and accessing a few of the entries can be 200 times slower than accessing the hash directly.

This is a potential security issue; building OpenStruct from untrusted user data (e.g. JSON web request) may be susceptible to a “symbol denial of service” attack since the keys create methods and names of methods are never garbage collected.

This may also be the source of incompatibilities between Ruby versions:

o = OpenStruct.new
o.then # => nil in Ruby < 2.6, enumerator for Ruby >= 2.6

Builtin methods may be overwritten this way, which may be a source of bugs or security issues:

o = OpenStruct.new
o.methods # => [:to_h, :marshal_load, :marshal_dump, :each_pair, ...
o.methods = [:foo, :bar]
o.methods # => [:foo, :bar]

To help remedy clashes, OpenStruct uses only protected/private methods ending with `!` and defines aliases for builtin public methods by adding a `!`:

o = OpenStruct.new(make: 'Bentley', class: :luxury)
o.class # => :luxury
o.class! # => OpenStruct

It is recommended (but not enforced) to not use fields ending in `!`; Note that a subclass' methods may not be overwritten, nor can OpenStruct's own methods ending with `!`.

For all these reasons, consider not using OpenStruct at all.

Constant Summary collapse

VERSION =
"0.4.0"
InspectKey =

:nodoc:

:__inspect_key__

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(hash = nil) ⇒ OpenStruct

Creates a new OpenStruct object. By default, the resulting OpenStruct object will have no attributes.

The optional hash, if given, will generate attributes and values (can be a Hash, an OpenStruct or a Struct). For example:

require "ostruct"
hash = { "country" => "Australia", :capital => "Canberra" }
data = OpenStruct.new(hash)

data   # => #<OpenStruct country="Australia", capital="Canberra">

126
127
128
129
130
131
132
# File 'lib/ostruct.rb', line 126

def initialize(hash=nil)
  if hash
    update_to_values!(hash)
  else
    @table = {}
  end
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(mid, *args) ⇒ Object (private)

:nodoc:


253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
# File 'lib/ostruct.rb', line 253

private def method_missing(mid, *args) # :nodoc:
  len = args.length
  if mname = mid[/.*(?==\z)/m]
    if len != 1
      raise! ArgumentError, "wrong number of arguments (given #{len}, expected 1)", caller(1)
    end
    set_ostruct_member_value!(mname, args[0])
  elsif len == 0
    @table[mid]
  else
    begin
      super
    rescue NoMethodError => err
      err.backtrace.shift
      raise!
    end
  end
end

Instance Attribute Details

#tableObject (readonly) Also known as: table!

:nodoc:


385
386
387
# File 'lib/ostruct.rb', line 385

def table
  @table
end

Instance Method Details

#==(other) ⇒ Object

Compares this object and other for equality. An OpenStruct is equal to other when other is an OpenStruct and the two objects' Hash tables are equal.

require "ostruct"
first_pet  = OpenStruct.new("name" => "Rowdy")
second_pet = OpenStruct.new(:name  => "Rowdy")
third_pet  = OpenStruct.new("name" => "Rowdy", :age => nil)

first_pet == second_pet   # => true
first_pet == third_pet    # => false

402
403
404
405
# File 'lib/ostruct.rb', line 402

def ==(other)
  return false unless other.kind_of?(OpenStruct)
  @table == other.table!
end

#[](name) ⇒ Object

:call-seq:

ostruct[name]  -> object

Returns the value of an attribute, or `nil` if there is no such attribute.

require "ostruct"
person = OpenStruct.new("name" => "John Smith", "age" => 70)
person[:age]   # => 70, same as person.age

282
283
284
# File 'lib/ostruct.rb', line 282

def [](name)
  @table[name.to_sym]
end

#[]=(name, value) ⇒ Object Also known as: set_ostruct_member_value!

:call-seq:

ostruct[name] = obj  -> obj

Sets the value of an attribute.

require "ostruct"
person = OpenStruct.new("name" => "John Smith", "age" => 70)
person[:age] = 42   # equivalent to person.age = 42
person.age          # => 42

297
298
299
300
301
# File 'lib/ostruct.rb', line 297

def []=(name, value)
  name = name.to_sym
  new_ostruct_member!(name)
  @table[name] = value
end

#delete_field(name) ⇒ Object

Removes the named field from the object and returns the value the field contained if it was defined. You may optionally provide a block. If the field is not defined, the result of the block is returned, or a NameError is raised if no block was given.

require "ostruct"

person = OpenStruct.new(name: "John", age: 70, pension: 300)

person.delete_field!("age")  # => 70
person                       # => #<OpenStruct name="John", pension=300>

Setting the value to nil will not remove the attribute:

person.pension = nil
person                 # => #<OpenStruct name="John", pension=nil>

person.delete_field('number')  # => NameError

person.delete_field('number') { 8675_309 } # => 8675309

350
351
352
353
354
355
356
357
358
359
360
# File 'lib/ostruct.rb', line 350

def delete_field(name)
  sym = name.to_sym
  begin
    singleton_class.remove_method(sym, "#{sym}=")
  rescue NameError
  end
  @table.delete(sym) do
    return yield if block_given!
    raise! NameError.new("no field `#{sym}' in #{self}", sym)
  end
end

#dig(name, *names) ⇒ Object

:call-seq:

ostruct.dig(name, *identifiers) -> object

Finds and returns the object in nested objects that is specified by name and identifiers. The nested objects may be instances of various classes. See Dig Methods.

Examples:

require "ostruct"
address = OpenStruct.new("city" => "Anytown NC", "zip" => 12345)
person  = OpenStruct.new("name" => "John Smith", "address" => address)
person.dig(:address, "zip") # => 12345
person.dig(:business_address, "zip") # => nil

319
320
321
322
323
324
325
326
# File 'lib/ostruct.rb', line 319

def dig(name, *names)
  begin
    name = name.to_sym
  rescue NoMethodError
    raise! TypeError, "#{name} is not a symbol nor a string"
  end
  @table.dig(name, *names)
end

#each_pairObject

:call-seq:

ostruct.each_pair {|name, value| block }  -> ostruct
ostruct.each_pair                         -> Enumerator

Yields all attributes (as symbols) along with the corresponding values or returns an enumerator if no block is given.

require "ostruct"
data = OpenStruct.new("country" => "Australia", :capital => "Canberra")
data.each_pair.to_a   # => [[:country, "Australia"], [:capital, "Canberra"]]

199
200
201
202
203
# File 'lib/ostruct.rb', line 199

def each_pair
  return to_enum(__method__) { @table.size } unless block_given!
  @table.each_pair{|p| yield p}
  self
end

#encode_with(coder) ⇒ Object

Provides marshalling support for use by the YAML library.


425
426
427
428
429
430
431
432
433
# File 'lib/ostruct.rb', line 425

def encode_with(coder) # :nodoc:
  @table.each_pair do |key, value|
    coder[key.to_s] = value
  end
  if @table.size == 1 && @table.key?(:table) # support for legacy format
    # in the very unlikely case of a single entry called 'table'
    coder['legacy_support!'] = true # add a bogus second entry
  end
end

#eql?(other) ⇒ Boolean

Compares this object and other for equality. An OpenStruct is eql? to other when other is an OpenStruct and the two objects' Hash tables are eql?.

Returns:

  • (Boolean)

412
413
414
415
# File 'lib/ostruct.rb', line 412

def eql?(other)
  return false unless other.kind_of?(OpenStruct)
  @table.eql?(other.table!)
end

#freezeObject


248
249
250
251
# File 'lib/ostruct.rb', line 248

def freeze
  @table.freeze
  super
end

#hashObject

Computes a hash code for this OpenStruct.


418
419
420
# File 'lib/ostruct.rb', line 418

def hash # :nodoc:
  @table.hash
end

#init_with(coder) ⇒ Object

Provides marshalling support for use by the YAML library.


438
439
440
441
442
443
444
445
446
447
# File 'lib/ostruct.rb', line 438

def init_with(coder) # :nodoc:
  h = coder.map
  if h.size == 1 # support for legacy format
    key, val = h.first
    if key == 'table'
      h = val
    end
  end
  update_to_values!(h)
end

#inspectObject Also known as: to_s

Returns a string containing a detailed summary of the keys and values.


367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
# File 'lib/ostruct.rb', line 367

def inspect
  ids = (Thread.current[InspectKey] ||= [])
  if ids.include?(object_id)
    detail = ' ...'
  else
    ids << object_id
    begin
      detail = @table.map do |key, value|
        " #{key}=#{value.inspect}"
      end.join(',')
    ensure
      ids.pop
    end
  end
  ['#<', self.class!, detail, '>'].join
end

#marshal_dumpObject

Provides marshalling support for use by the Marshal library.


208
209
210
# File 'lib/ostruct.rb', line 208

def marshal_dump # :nodoc:
  @table
end

#to_h(&block) ⇒ Object


170
171
172
173
174
175
176
# File 'lib/ostruct.rb', line 170

def to_h(&block)
  if block
    @table.to_h(&block)
  else
    @table.dup
  end
end