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.pension = 300

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

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

australia = OpenStruct.new(:country => "Australia", :population => 20_000_000)
p australia   # -> <OpenStruct country="Australia" population=20000000>

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

measurements = OpenStruct.new("length (in inches)" => 24)
measurements.send("length (in inches)")  # -> 24

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

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

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

first_pet == second_pet   # -> false

first_pet.delete_field(:owner)
first_pet == second_pet   # -> true

Implementation:

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

Constant Summary collapse

InspectKey =

:nodoc:

:__inspect_key__

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", :population => 20_000_000 }
data = OpenStruct.new(hash)

p data        # -> <OpenStruct country="Australia" population=20000000>

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# File 'lib/ostruct.rb', line 87

def initialize(hash=nil)
  @table = {}
  if hash
    hash.each_pair do |k, v|
      k = k.to_sym
      @table[k] = v
      new_ostruct_member(k)
    end
  end
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(mid, *args) ⇒ Object

:nodoc:


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# File 'lib/ostruct.rb', line 176

def method_missing(mid, *args) # :nodoc:
  mname = mid.id2name
  len = args.length
  if mname.chomp!('=')
    if len != 1
      raise ArgumentError, "wrong number of arguments (#{len} for 1)", caller(1)
    end
    modifiable[new_ostruct_member(mname)] = args[0]
  elsif len == 0
    @table[mid]
  else
    raise NoMethodError, "undefined method `#{mid}' for #{self}", caller(1)
  end
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.


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# File 'lib/ostruct.rb', line 263

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

#[](name) ⇒ Object

Returns the value of a member.

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

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# File 'lib/ostruct.rb', line 196

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

#[]=(name, value) ⇒ Object

Sets the value of a member.

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

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# File 'lib/ostruct.rb', line 207

def []=(name, value)
  modifiable[new_ostruct_member(name)] = value
end

#delete_field(name) ⇒ Object

Remove the named field from the object. Returns the value that the field contained if it was defined.

require 'ostruct'

person = OpenStruct.new('name' => 'John Smith', 'age' => 70)

person.delete_field('name')  # => 'John Smith'

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# File 'lib/ostruct.rb', line 221

def delete_field(name)
  sym = name.to_sym
  singleton_class.__send__(:remove_method, sym, "#{name}=")
  @table.delete sym
end

#each_pairObject

Yields all attributes (as a symbol) along with the corresponding values or returns an enumerator if not block is given. Example:

require 'ostruct'
data = OpenStruct.new("country" => "Australia", :population => 20_000_000)
data.each_pair.to_a  # => [[:country, "Australia"], [:population, 20000000]]

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# File 'lib/ostruct.rb', line 127

def each_pair
  return to_enum __method__ unless block_given?
  @table.each_pair{|p| yield p}
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?.


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# File 'lib/ostruct.rb', line 273

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

#hashObject

Compute a hash-code for this OpenStruct. Two hashes with the same content will have the same hash code (and will be eql?).


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# File 'lib/ostruct.rb', line 281

def hash
  @table.hash
end

#initialize_copy(orig) ⇒ Object

Duplicate an OpenStruct object members.


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# File 'lib/ostruct.rb', line 99

def initialize_copy(orig)
  super
  @table = @table.dup
  @table.each_key{|key| new_ostruct_member(key)}
end

#inspectObject Also known as: to_s

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


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# File 'lib/ostruct.rb', line 232

def inspect
  str = "#<#{self.class}"

  ids = (Thread.current[InspectKey] ||= [])
  if ids.include?(object_id)
    return str << ' ...>'
  end

  ids << object_id
  begin
    first = true
    for k,v in @table
      str << "," unless first
      first = false
      str << " #{k}=#{v.inspect}"
    end
    return str << '>'
  ensure
    ids.pop
  end
end

#marshal_dumpObject

Provides marshalling support for use by the Marshal library.


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# File 'lib/ostruct.rb', line 135

def marshal_dump
  @table
end

#marshal_load(x) ⇒ Object

Provides marshalling support for use by the Marshal library.


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# File 'lib/ostruct.rb', line 142

def marshal_load(x)
  @table = x
  @table.each_key{|key| new_ostruct_member(key)}
end

#to_hObject

Converts the OpenStruct to a hash with keys representing each attribute (as symbols) and their corresponding values Example:

require 'ostruct'
data = OpenStruct.new("country" => "Australia", :population => 20_000_000)
data.to_h   # => {:country => "Australia", :population => 20000000 }

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# File 'lib/ostruct.rb', line 114

def to_h
  @table.dup
end