How to Make Deep Copies in Ruby

How to Make Deep Copies in Ruby Its often necessary to make a copy of a value in Ruby. While this may seem simple, and it is for simple objects, as soon as you have to make a copy of a data structure with multiple array or hashes on the same object, you will quickly find there are many pitfalls. Objects and References To understand whats going on, lets look at some simple code. First, the assignment operator using a POD (Plain Old Data) type in Ruby. a 1b aa 1puts b Here, the assignment operator is making a copy of the value of a and assigning it to b using the assignment operator. Any changes to a wont be reflected in b. But what about something more complex? Consider this. a [1,2]b aa 3puts b.inspect Before running the above program, try to guess what the output will be and why. This is not the same as the previous example, changes made to a are reflected in b, but why? This is because the Array object is not a POD type. The assignment operator doesnt make a copy of the value, it simply copies the reference to the Array object. The a and b variables are now references to the same Array object, any changes in either variable will be seen in the other. And now you can see why copying non-trivial objects with references to other objects can be tricky. If you simply make a copy of the object, youre just copying the references to the deeper objects, so your copy is referred to as a shallow copy. What Ruby Provides: dup and clone Ruby does provide two methods for making copies of objects, including one that can be made to do deep copies. The Object#dup method will make a shallow copy of an object. To achieve this, the dup method will call the initialize_copy method of that class. What this does exactly is dependent on the class. In some classes, such as Array, it will initialize a new array with the same members as the original array. This, however, is not a deep copy. Consider the following. a [1,2]b a.dupa 3puts b.inspecta [ [1,2] ]b a.dupa[0] 3puts b.inspect What has happened here? The Array#initialize_copy method will indeed make a copy of an Array, but that copy is itself a shallow copy. If you have any other non-POD types in your array, using dup will only be a partially deep copy. It will only be as deep as the first array, any deeper arrays, hashes or other objects will only be shallow copied. There is another method worth mentioning, clone. The clone method does the same thing as dup with one important distinction: its expected that objects will override this method with one that can do deep copies. So in practice what does this mean? It means each of your classes can define a clone method that will make a deep copy of that object. It also means you have to write a clone method for each and every class you make. A Trick: Marshalling Marshalling an object is another way of saying serializing an object. In other words, turn that object into a character stream that can be written to a file that you can unmarshal or unserialize later to get the same object. This can be exploited to get a deep copy of any object. a [ [1,2] ]b Marshal.load( Marshal.dump(a) )a[0] 3puts b.inspect What has happened here? Marshal.dump creates a dump of the nested array stored in a. This dump is a binary character string intended to be stored in a file. It houses the full contents of the array, a complete deep copy. Next, Marshal.load does the opposite. It parses this binary character array and creates a completely new Array, with completely new Array elements. But this is a trick. Its inefficient, it wont work on all objects (what happens if you try to clone a network connection in this way?) and its probably not terribly fast. However, it is the easiest way to make deep copies short of custom initialize_copy or clone methods. Also, the same thing can be done with methods like to_yaml or to_xml if you have libraries loaded to support them.

Analysis of Batter My Heart Essays

Analysis of Batter My Heart Essays Analysis of Batter My Heart Paper Analysis of Batter My Heart Paper In the poem â€Å"Batter my heart, three-personed God†, John Donne portrays a troubled speaker who is experiencing a spiritual disturbance in accepting his current faith and who is therefore expressing his desire to renew his faith in God and his religion. Throughout this religious sonnet, Donne employs the use of metaphors which provide clues as to what the speaker is feeling during the poem and paradoxes to exemplify the speaker’s request. Based on the first statement of the poem alone, it is clear that the lines to follow will involve some sort of religious conflict, as shown by the command said by the speaker, â€Å"Batter my heart, three-personed God†. In relation to the rest of the poem, one can conclude that the â€Å"three-personed God† to which the speaker is referring is a metaphor for the Holy Trinity of the Christian religion; the use of the word â€Å"batter† serves as a forerunner to the later violent requests of the speaker. The simile used in line 5 of the poem which compares the speaker to a usurped town shows that the speaker is in an undesired and vulnerable position, just as a city would be just after being appropriated by a foreign enemy. In this metaphorical sense, the speaker is asking God to defend him and reclaim him from this unknown enemy. This idea can be later confirmed in lines 7 and 8 where the speaker directly speaks of God’s attempt to â€Å"recapture† his soul. Although this acknowledgement of a divine intervention is evident to the speaker, he nonetheless states that â€Å"Reason, [God’s] viceroy in me†¦/ proves weak or untrue,† and that this instrument of God has itself been â€Å"captived†. As a result of this lack of faith, the speaker states that his efforts to accept God have been futile when faced with this â€Å"enemy†. The usage of metaphors and similes within the poem have the overall effect of helping to set up the condition of the speaker in order to provide reason for his request.

International Affairs Essay Example | Topics and Well Written Essays - 500 words

International Affairs - Essay Example She graduated from Concordia College in Moorhead, Minn., with degrees in mass communication and French and with dreams of being an international correspondent. She said that her goal as Miss North Dakota was to encourage people to appreciate cultural differences. When she received her Miss North Dakota title, Ms Saberi said that her aim was to encourage other people to appreciate cultural differences - an ambition that eventually led her into a career in journalism. TEHRAN, Iran (AP) -- Iran convicted an American journalist of spying for the United States and sentenced her to eight years in prison, her lawyer said Saturday, complicating the Obama administrations efforts to break a 30-year-old diplomatic deadlock with Tehran. The White House said President Barack Obama was "deeply disappointed" by the conviction, while the journalists father told a radio station his daughter was tricked into making incriminating statements by officials who told her they would free her if she did. Roxana Saberi, a 31-year-old dual American-Iranian citizen, was arrested in late January and initially accused of working without press credentials. But earlier this month, an Iranian judge leveled a far more serious allegation, charging her with spying for the United States. The Fargo, North Dakota native had been living in Iran for six years and had worked as a freelance reporter for several news organizations including National Public Radio and the British Broadcasting Corp. The journalists Iranian-born father, Reza Saberi, told NPR that his daughter was convicted Wednesday, two days after she appeared before an Iranian court in an unusually swift one-day closed-door trial. The court waited until Saturday to announce its decision to the lawyers, he said. Saberis father is in Iran but was not allowed into the courtroom to see his daughter, who he described as "quite depressed." He said she denied the incriminating